Here are some sonic flash games, however many are only loosely related to sonic. For instance sonic snake has a picture of sonic in the background, normal snake gameplay. The best game is ultimate sonic, which is listed as sonic flash below and should be the game that loads up when you go on the link. It's a sonic clone, with many levels etc. Basic sonic is good but only lasts one short level. The other games can be found with the links to the right of the screen.

http://www.sonicgame.info/

Sonic Flash
Super Smash Flash
Sonic Blox
Angel Island
Shadow Flash
Sonica
Mega Collection+
Sonic Knuckles Pacman
Sonic 3D Snowboard
Sonic Boom
Sonic Millionaire
Final Fantasy x5
Heroes Puzzle
Sonic Snake
Sonic Sliding Puzzle
Sonic Puzzle
Shadow Sonic Puzzle
Sonic Designer
Sonic Racer
Sonicx Rings
Shadowx Rings
Sonic Bowling
Basic Sonic
Sonic Lost in Mario World