Guitar Hero on my iPod (well almost). And only £4.99 in the UK iTunes store.
Wow this game is addictive. I’ve mostly been playing the drum version of it, which despite what this review says, I find much easier than the guitar one as you only have three “pads” to worry about (well, four, but two function identically).
It can get a tiny bit laggy when the song gets frantic (Message in a Bottle on Expert drums mode, anybody?) and it does eat the battery power, but I have now put off purchasing that Xbox for a little while 