The UFC recently made a list of the 100 greatest fights of all time.

You could go to their website and look for the dvd which would have the list of those fights.

Then youtube the fights lol

My suggestions would be:

Wanderlei Silva vs. Chuck Liddell

Matt Hughes vs. Carlos Newton

Matt Hughes vs. Frank Trigg I & II

Anderson Silva vs. Chris Leben

GSP vs. Matt Serra I & II

Randy Couture vs. Tito Ortiz