http://playr.org
"Get nostalgic with some old school games!"
Playr is a website you can go to to play old school games for gameboy color and other systems. There's tons to play, like Fighting, Roleplaying, Racing, Shooting, Action, Adventure, Platform, etc. And best of all, you can play them all for free! All you have to do is make an account.
I'm currently playing Pokemon Gold, Pokemon Yellow, and Pokemon Blue.