Well if you can count Part 1 and Part 2 as one 29-minute track, then I would say Rush's "Cygnus X-1" is my favorite. I like having the most bang for my buck, so if I can't do that I would say it's a tie between "The Gates Of Delirium" by Yes and Genesis's "Supper's Ready."
How's THAT for bending the rules!
