I was just at Circuit City the other day looking for a DS. I didn't find one (of course) but I did spot Guitar Hero II. I'd heard lots of good things about this game, so I bought it.
Freakin'. Awesome.
I love this game. It's like DDR for guitarists. And the song selection is great. Pretty much everything is either classic rock or stuff that hasn't been considered new since I was in middle or highschool. So it's mostly pretty familiar stuff. The only gripe I have with it is I wish there was a way to just listen to a song so I could get an idea of how the unfamiliar ones go without having to play along. That, and after a couple hours of play, my left hand feels like it's about ready to fall off. But that just means i'm rocking hard enough.