my favorite track of all time of any of the games ive done is the main track off of Time Fcuk.
http://www.youtube.com/watch?v=PjIfMrTMxFU
its even more powerful with the lead in track, this track didnt totaly fade in till the tutorial levels ended. i also really love the new track he did for the 2nd chapter in the basement collection.
Other Personal faves
Betus Blues (SMB)- http://www.youtube.com/watch?v=6Kf7ycHajX4
Egypt Theme (Gish)- http://www.youtube.com/watch?v=xnYweOV98ok
March of the Smallest Feet (triachnid)- http://www.youtube.com/watch?v=Gy4nKwWd6cI
my new favorite tracks are on the mewgenics soundtrack, there are a few very moody and cool tracks. we might upload a really upbeat one next caturday for everyone to check out.
this is a public one thats allways stuck in my head when testing Mew
The Ballad of D.Claude (mewgenics)- http://www.youtube.com/watch?v=7X830jaEkf4