Audio Surf, though not necessarily an RTS, is close enough. AS is... well, a sort of crude mix of Guitar Hero and Tetris, except the game will recognize and play correctly any song you have on your computer, unlike GH, which gives you the songs you are allowed to play. AS is extremely impressive for its ability to play any song.
There is also a nice High Scores system that puts you up according to the difficulty level you played on against the World, then your country (or state if in the US), and your friends.
I highly suggest this game to everyone, plus you can't go wrong since it's only $9.95!
