Sonic burst onto the game scene in 1991, and fast became Sega's official mascot. Sega Genesis had been looking for something to rival Nintendo's Super Mario Brothers. They put together a team to come with an idea and several were submitted....one of which was Teddy Roosevelt in pajamas(that idea later became the inspiration for the main villain in the games, Dr. Ivor Robotnik). Luckily for them, and Sega players, the blue hedgehog won out. And over the course of 15 years, there's been several different Sonic games. Including games based on different characters in Sonic, but Sonic was never feautured in them. The following is a list of pretty much all the different Sonic titles that have been released over the past 15 years. You can check out Amazon.com if you have one of the systems listed with the games to buy that one. Alot of the games are probably outdated and no longer available, but it's interesting to see just how many titles this series has had...on all the various game systems.
 
Country Key
J = Japan
N = North America
E = PAL (Europe, Asia, Australia, Brazil)
X = PAL excluding Brazil
B = Brazil ONLY

Official games involving Sonic the Hedgehog (or related characters thereof)
For the Sega Mega Drive/Sega Genesis:
Sonic the Hedgehog (JNE)
Sonic the Hedgehog 2 (JNE)
Sonic the Hedgehog Spinball (also Sonic Spinball) (JNE)
Dr. Robotnik's Mean Bean Machine (NE)
Sonic the Hedgehog 3 (JNE)
Sonic & Knuckles (JNE)
Sonic 3D Blast (aka Sonic 3D: Flickies' Island or Sonic 3D Blast: Flickie's Island) (NE)
Sonic Compilation/Sonic Classics 3-in-1 (contains Sonic the Hedgehog, Dr. Robotnik's Mean Bean Machine, and Sonic the Hedgehog 2) (NE)

For the Sega Master System:
Sonic the Hedgehog (NE)
Sonic the Hedgehog 2 (E)
Sonic Chaos (E)    
Sonic Spinball (E)    
Dr. Robotnik's Mean Bean Machine (E)    
Sonic Blast (E)
 
For Sega Mega-CD/Sega CD:
Sonic the Hedgehog CD (aka Sonic CD) (JNE)

For the Sega Game Gear:
Sonic the Hedgehog (JNX)
Sonic the Hedgehog 2 (JNX)
Sonic Chaos (aka Sonic & Tails) (JNX)
Sonic Spinball (NX)
Dr. Robotnik's Mean Bean Machine (NX)
Sonic Drift (J)
Sonic Triple Trouble (aka Sonic & Tails 2) (JNE)
Sonic Drift 2 (JNE)
Tails Adventures (as an item)(JNE)
Sonic 2 In 1 (contains Sonic the Hedgehog 2 and Sonic Spinball (Game Gear version)) (N)
Sonic Labyrinth (JNE)
Tails' Skypatrol (J)
Sonic Blast (aka G-Sonic) (JNX)

For the Sega Pico:
Sonic's Gameworld (JN)
Tails And The Music Maker (JN)

For the Sega Meganet Modem:
Sonic Eraser (J)

For the Sega 32X:
Knuckles' Chaotix (aka Chaotix) (cameo)(JNE)

For the Sega Saturn:
Sonic Jam (JNE)
Sonic R (JNE)
Sonic 3D Blast (aka Sonic 3D: Flickies' Island or Sonic 3D Blast: Flickies' Island) (JNE)

For the Sega Dreamcast:
Sonic Adventure (J)
Sonic Adventure International (outside of Japan this version is just Sonic Adventure) (JNE)
Sonic Shuffle (JNE)
Sonic Adventure 2 (JNE)
Sonic the Hedgehog (Sega Smash Pack) (N)

For the PC:
Sonic Schoolhouse (N)
Sonic 3D Blast (a port of the Sega Saturn version) (NE)
Sonic the Hedgehog CD (aka Sonic CD) (JNE)
Sonic & Knuckles Collection (a combination of the Sega Genesis games Sonic 3, S&K and S3&K) (JNE)
Sonic R (JNE)
Sonic Adventure DX: Director's Cut (JE)
Sonic the Hedgehog (RealArcade) (N)
Sonic the Hedgehog 2 (RealArcade, Sega Smash Pack 2)(N)
Sonic the Hedgehog Spinball (RealArcade, Sega Smash Pack) (N)
Dr. Robotnik's Mean Bean Machine (RealArcade, Sega Puzzle Pack)(N)
Sonic the Hedgehog 3 (RealArcade) (N)
Sonic & Knuckles (RealArcade) (N)
Sonic 3D Blast (RealArcade (port of Sega Genesis version)) (NE)
Sonic Heroes (JNE)

For SNK Neo Geo Pocket Color:
Sonic the Hedgehog Pocket Adventure (JNE)

For Nintendo Game Boy Advance:
Sonic Advance (JNE)
Sonic Advance 2 (JNE)
Sonic Pinball Party (JNE)
Sonic Battle (JNE)
Sonic Advance 3 (JNE)

For Nintendo GameCube:
Sonic Adventure 2: Battle (JNE)
Sonic Mega Collection (NJE)
Sonic Adventure DX: Director's Cut (NJE)
Sonic Heroes (JNE)
Shadow the Hedgehog
Sonic Gems Collection (JNE)
Sonic Riders

For Sony PlayStation 2:
Sonic Heroes (JNE)
Sonic Mega Collection Plus (JNE)
Sega Superstars
Shadow the Hedgehog
Sonic Gems Collection (JE)
Sonic Riders

For Nintendo DS:
Sonic Rush

For Xbox:
Sonic Heroes (JNE)
Sonic Mega Collection Plus (JNE)
Shadow the Hedgehog
Sonic Riders

For Xbox 360:
Sonic the Hedgehog (tentative title)

For Sony PlayStation 3:
Sonic the Hedgehog (tentative title)

For Nokia N-Gage:
SonicN (NE)

For arcade:
Waku Waku Sonic Patrol Car (J)
Sega Sonic Cosmo Fighter Galaxy Patrol] (J)
SegaSonic the Hedgehog (J)
Sonic the Fighters (aka Sonic Championship) (JN)
Sonic and Tails Spinner (N)
CR Sonic (J)

For Tiger Game.com:
Sonic Jam (N)

For Mobile Phones:
Sonic the Hedgehog (J) - For NTT DoCoMo i-mode 503 / 504
Sonic Tennis (J) - For Vodafone and NTT DoCoMo i-mode 503 / 504 / 505 / 900
Sonic Golf (J) - For NTT DoCoMo i-mode 503 / 504
Speed (J) - For NTT DoCoMo i-mode 503 / 504
Speed DX (J) - For Vodafone and NTT DoCoMo i-mode 505 / 900
Sonic Fishing (J) - For NTT DoCoMo i-mode 503 / 504
Sonic Billiards (J) - For Vodafone and NTT DoCoMo i-mode 503 / 504
Nakayoshi Chao (J) - For NTT DoCoMo i-mode 504
Sonic Bowling (J) - For NTT DoCoMo i-mode 503 / 504
Sonic No Jirai Sagashi Game (J) - For NTT DoCoMo i-mode 503 / 504
Sonic Racing Shift Up (J) - For NTT DoCoMo i-mode 503 / 504
Sonic Putter (J) - For NTT DoCoMo i-mode 503 / 504
Sonic Darts (J) - For NTT DoCoMo i-mode 503 / 504
Sonic Racing Kart (J) - For NTT DoCoMo i-mode 503 / 504 / 505 / 900
Sonic Reversi (J) - For NTT DoCoMo i-mode 503 / 504 / 505
Tails No Flying Get (J) - NTT DoCoMo i-mode 504 / 505 / 900
Sonic Hopping (J) - NTT DoCoMo i-mode 503 / 504 / 505 / 900
Sonic Hopping 2 (J) - NTT DoCoMo i-mode 503 / 504 / 505 / 900

For Palm OS:
Sonic the Hedgehog (N)
Dr. Robotnik's Mean Bean Machine (N)

Other games featuring Sonic characters:
(Cameo appearances)
Art Alive (An art game. Sonic appears as "stamps" to be placed.)
Beach Spikers (A giant inflatable Sonic floats above one of the volleyball courts)
Blue Stinger (A store is occupied by copies of Sonic Adventure.)
Bug! (One of the game's bonus stages features the character, Bug, racing against Sonic.)
Christmas NiGHTS (One of the presents is to play as Sonic in the Spring Valley Time Attack)
Clockwork Knight 2 (In a hidden movie, a Sonic toy can be seen sitting on a shelf.)
Crusader of Centy (a.k.a. Soleil) (An action RPG. In a small beach, Sonic lays in a lawn chair. Talk to Sonic and he says: "Tsk, tsk. I'm a gallant hedgehog. Don't mess or you'll get burned.")
Donkey Kong Country 2 (At the end of the game, Diddy gets rated as a video game hero according to how many of the DK Coins you collect. On the screen is a trash can labeled "No Hopers" with Sonic's shoes and Earthworm Jim's gun next to it.)
Daytona USA (A racing title, Sonic appears carved in a stone mountain on the Three-Seven Speedway course.)
F1 World Championship: Beyond the Limit (Sonic and Tails' heads can be spotted on billboards on some tracks.)
Feel the Magic XY/XX (Sonic and Chao wigs are unlockable for the main female character)
Fighters Megamix (Bark the Polarbear and Bean the Dynamite are unlockable fighters)
Fighting Vipers (In the intro movie, Sanman's pile of toys contains a model of the Lunar Fox, the spaceship Tails creates in Sonic the Fighters.)
Flicky (The blue bird character, Flicky, became one of many animals that Sonic rescues in the classic games after his appearance in this game, with Sonic 3D Blast borrowing heavily from some aspects of the gameplay)
Gale Racer (A racing game. A Sonic keychain hangs on the rearview mirror.)
Illbleed (One of the bosses, Zodick, resembles a monstrous Sonic and even drops rings when hit)
LA Machineguns (Sonic and the Sonic Adventure logo appear as neon signs in the Las Vegas stage.)
Last Bronx (In Tommy's stage, there is a poster of Sonic on a building in the background. Also, there's a sticker of Sonic on Tommy's outfit.)
Le Mans 24 (Sonic is a hidden racer.)
Metal Head (Sonic appears on a billboard in the scenery.)
NBA 2K (Players can create a team called the Hedgehogs, which features Sonic holding a basketball as the logo.)
NHL 2K (Sonic appears on the Jumbotron occasionally.)
Outrunners (Another racing title, in the intro Sonic and Tails fly in two versions of their biplane, the Tornado, and sprinkle the Sega logo. In the game, Sonic billboards appear off to the sides.)
Phantasy Star IV (A book in the grammar school is about Sonic)
Phantasy Star Online (Sonic, Knuckles, and Tails have cameoed online numerous times.)
Popful Mail (The main character Mail examines a billboard in the game, which has a small drawing of Sonic off to the side.)
RadMobile (an arcade game, Sonic dangles from the rear view mirror)
Scud Race (Sonic appears on a billboard in the Beginner track.)
Sega Bass Fishing (In the Dreamcast version, after a few courses you receive a Sonic lure.)
Sega Game Pack 4 in 1 (Sonic is the umpire in the tennis game)
Sega Superstars (A game for the PS2 EyeToy camera. It features a Sonic minigame)
Shenmue (Sonic character dolls are available.)
Shining Force II (A hidden all-boss battle at the end has the map in the shape of Sonic's body)
Spider-Man for Sega CD (In the game's ending, a carving of Sonic's head can be spotted on a cave in the background.)
Spikeout (Sonic appears near an elevator in one of the levels.)
Tamagotchi on Sega Saturn (Treat your tamagotchi right, and it'll become a Sonagotchi.)
Tom & Jerry: The Movie for Game Gear (An ad for Sonic appears on the windows of a bookstore in one level.)
Toy Commander (Sonic appears on a calendar on the floor in some stages.)
Ultimate Soccer (Sonic represents a console-controlled team in the menus)
Virtua Fighter 2 (In the Saturn version, when Jacky Bryant and Sarah Bryant fight, a hidden stage called Chicago is chosen. There's a brick wall in the background with graffiti, including a doodle of Sonic.)
Virtua Fighter 4: Evolution (In Quest Mode, one of the fighting tournaments is called the Sonic Cup. The logo features a picture of Sonic with rings glowing around him.)
Virtua Fighter Kids (Same as Virtua Fighter 2's cameo.)
Virtua Striker 2 (A hidden team has Bean the Dynamite and a slew of other weird characters.)
Virtua Striker 3 (A hidden team has Sonic, Tails, Knuckles, Amy, Dr. Eggman, and a Chao as players, with Yuji Naka as the coach)
Wacky Worlds (Another art title, this game is composed entirely of stamp placement. Sonic and Tails are on the game's cover, Sonic is in a spaceship and is your cursor to select a world to play in, and Tails is a stamp in the jungle area.)
Waverunner (Sonic appears on the back of a racer's lifejacket.)

Demonstrations
Sonic the Hedgehog for the Game Boy - a demonstration program
Sonic E3 for the Nintendo DS - a demonstration shown at E3

Unfinished / Unreleased

Sonic Crackers / Sonic Studium - Sega Megadrive / Sega Genesis (A similar concept was later used in Knuckles' Chaotix)
Sonic Xtreme - Sega Saturn
Sonic The Hedgehog 4

Pirated/unlicensed games which are direct ripoffs of Sonic and other games:
Somari, an unlicensed version of Sonic the Hedgehog that was ported to the Famicom and instead stars Somari, an altered Mario; the game is from Hong Kong
Family Kid, an edited version of Somari.
Sonic Jam 6, a hacked version of an unlicensed version of Super Mario Bros. using tiles from Super Mario Collection; the game is from China
Sonic the Hedgehog 4 (actually a Speedy Gonzalez game for the Super Nintendo)
Sonic the Hedgehog 6 (another Speedy Gonzalez game for the Game Boy)
Sonic the Hedgehog (Amiga)
Sonyc, a very well made unlicensed game, both MSX2 and GBA versions
Jurassic Boy 2, a blatant rip-off of the Sonic series for the GBC.

The following games are often mistaken for pirate games, but are actually ROM hacks by Yuski the Dog:
Sonic-Boy in Monsterland, hacked version of Wonder Boy in Monster Land for the Sega Master System
Sonic-Boy in Monsterland 2 - Eggman's Trap, hacked version of Wonder Boy in Monster Land 3 for the Sega Master System
Sonic-Boy in Monsterland 3 - Eggman's Room, hacked version of Geraldinho, a Teddy Boy clone for the Sega Master System
Sonic-Boy in Monsterland 4 - hacked version of Wonder Boy in Monster World
Sonic vs. Os. Mauniks, hacked version of a Psycho Fox clone for the Sega Master System

Sonic Fangames:
(The following are just some of the fangames. If I can find anymore titles, I'll post them here)
ChaoS
Chaos Battles
Crazy Cabbie Sonic
Dr. Robotniks Rebellion
King Of Mobius
Knuckles Blast
Knuckles Episode One Racer: Special Edition
Knuckles Millennium
Knuckles Millennium 2
Legendary SoniChaos
Little Chaos
Mario & Sonic
Mario & Sonic Return
Metal Sonic Quest: Special Edition
Metal Tails
Neo Sonic Boom
Neo Sonic Universe
ONMI Khaos
ShenSonic
Sonic & Friends
Sonic Avalanche
Sonic Dead-Zone
Sonic Epoch Advance
Sonic Fight!
Sonic Fury X
Sonic Infinity Halloween
Sonic MADventure
Sonic Maze Mania
Sonic QTE
Sonic QTE²
Sonic Robo Blast 2 Halloween (DOS)
Sonic Robo Blast 2 Xmas
Sonic Robo Blast 2
Sonic Search
Sonic Stash
Sonic SV
Sonic The Hedgehog Fun Zone!
Sonic Ultra Compilation
Sonic Ultra: The Return
Sonic Ultra: The Return Deluxe
Sonic Ultra 3
Sonic Wars
Sonic World
Sonic World 2
Sonic World 3
Sonic X-treme
Sonic Y2K Unlimited
Sonic Y2K X-treme
Sonic Zero: Chapter One
Sonic: Tennis for Two
Sonic: The Fast Revelation
Sonic: The Search for Knuckles
Sonic: Time Attacked
SoniChaos
SoniChaos Revolution
Tails Flight to Flicky Island
Tails is Captured!
Tails Race
Tails Rescue Quest
Tale of Two Sonics
Thirdscape
Thirdscape 2
Thirdscape: Xmas Edition
Ultimate SoniChaos
Video Game Holiday
When Tails Gets Bored
Zone Racer