I usually have Dream Theater's Black Clouds and Silver Linings (or any of their albums) playing for just general racing and whatnot, along with Rush (anything), Queensryche, U2, Coheed and Cambria, and A Perfect Circle. When I want a change of pace, like for drifting, I put on my 70's/80's rock collection (Rush of that era, Motley Crue, Van Halen, Boston - the power ballads.)
If I'm doing racing for real or in a league, I put on Metallica, Iron Maiden, Green Day, Steve Vai, Joe Satriani and Pink Floyd... (Just seems to fit somehow.)
And if I'm in the mood for something slightly different, I slap on Marillion, Mumford & Sons, Big Gigantic, PSY, Dave Chappelle, The Cult, Yes, Triumph, and Your Favorite Martian.
(Yes, I've got a VERY large collection of music.