When it comes to victory songs, I like to stay with songs that are fast and fun from the get-go. It's your cooling-off period -- you've just poured blood, sweat and tears into a boss fight, and now you get to relax. Sit back, listen to the music, roll on loot, and feel like a badass.
My victory song would have to be something like Invaders Must Die by The Prodigy. I linked the song at the top of the post for anyone not familiar with it. It's what many people call a trailer song in that it is a tune that you hear in movie and game trailers frequently. For instance, you'll recognize Invaders Must Die from such trailers as Scott Pilgrim vs. The World and Duke Nukem Forever. It has a sordid past.
What is your victory song? Which song gets you rocked and ready for the next boss encounter or some good relaxing time after a night of hard work? Which song plays when the bar his 0%?