Flash Based Guitar Hero: Mucho Addictive
Here's a totally passable, Flash based verision of Guitar Hero so you can get your fix if you don't happen to be near the Playstation, X-box, Wii of your choice.
http://www.kongregate.com/games/Shinki/super-crazy-guitar-maniac-deluxe-...
It's played with the arrow keys and A, S, D. The songs are from complete unknowns due to copyright issues, but they're not completely horrible. It does make the game harder though, cause knowing the song well helps you get into the rhythmn.