Tetrisphere is a somewhat obscure, fun puzzle game with brilliant music. Try it out sometime!
This song plays when you start the game up, so I think of it as the main theme. Very awesome, and one of my favourite tracks.
Download link:
http://www.mediafire.com/?eqljlch5e2o0751
Download link for all the songs:
http://www.mediafire.com/?15qbawek8ly25
Neil Voss (soundtrack artist):
https://twitter.com/neilvoss