I can't possibly choose "the best tune" for me - there isn't simply such a thing (the same goes for games, books, movies, etc.).
Anyway, the first two pieces of music that come to mind when faced with such a question are (please excuse me if they've been mentioned already)
knulla-kuk!!! by Moby (Frédéric Motte) and the
Pinball Dreams intro music (whose name on the PC is "lightofday") by Blaizer (Olof Gustaffson): intricate, progressive musical composition, great vibes, high technical quality... pure excellence. But the same could be said of other modules by the same musicians or others...