Lets clarify.

I didn't really mean straight music. I meant "what tune would you want to play every time you walked into a room?". This could be any song, and I guess to an extent, lyrics. You could say:
The lyrics of Monty Python's "The Bright Side of Life" put to the tune of Twisted Sister's "Stay Hungry".
I have half-jokingly answered "The music from the underground levels of Super Mario Brothers" on occasion. So it really doesn't have to be a mainstream song or even a song really. Today I would say my theme song should be "The sound of hard drives clicking before permanent failure".