I just came across this gem on youtube, its a pancrase fight between Bas Rutten and Frank Shamrock.. it's pretty much the craziest thing I've ever seen.
YouTube - Bas Rutten vs Frank Shamrock
If this is about UFC specific fights, I highly suggest you check out:
Frankie Edgar vs Tyson Griffin
Randy Couture vs Tim Sylvia
Robbie Lawler vs Nick Diaz
Georges St.Pierre vs BJ Penn
Tank Abbott vs Steve Nelmark
Roger Huerta vs Leonard Garcia
Chuck Liddell vs Randy Couture (all three are good fights)
There are so many waaaaaay way back as well that are worth checking out. My best advice is watch all MMA, not just good fights.. I mean, you learn so much about the sport while watching even the most boring matches. Well at least I do anyway.. I watched Koscheck vs Sanchez probably four times.