Not sure if you've heard much about Guitar Hero [word redacted] ah, tribute Instant Jam, but basically it's a streaming browser thing that lets you play rhythm-action adaptations of theoretically any song for free. As long as you have it on your hard drive, buy the track from the game's store or use one of the built-in songs, anyway.
They've just opened it up to embedding on other sites - which means you can play the bally thing in its entirety below. A game! An actual game! Playable on RPS! We should do more of that. Have a play, then go shout obscure songs and impossible high scores at each other in the comments below. Let the great Kate Bush wars of 2008 begin again...
Worth noting I've shrunk the game slightly from its intended size to fit our page design, so if you hit any graphical/interface peculiarities it might be that. Seems to work OK here though. In terms of your own songs, it takes its time to add them, and the auto-gameification means you probably won't find the notes to be as neatly-matched as pre-tailored ones. But see how it goes.
But! What if you don't have any songs to play on this? Well, how about the theme tune to award-winning* games radio show and Friends Of RPS One Life Left? You'd like that, wouldn't you? Well, here you go.
* In the same way we're award-winning, anyway.