JamLegend. Not quite Guitar Hero but it's free!
We turned up with a number of things, which kept us occupied for about an hour, until we found JamLegend. It's kinda like guitar hero but you play it on your key board and it only has 3 notes. I believe you can plug in a Guitar Hero or Rock Band controller but I don't have one, so I guess that's up to you.
I believe that if if some one who has an account refers people (me, referring you,) then both people get "bonuses". http://www.jamlegend.com/refer/rf/272549 go here if you're interested, it's good fun and a great way to waste an hour or two.
XD ---- rock on!