My favorite fights off the top of my head:
BJ Penn vs Sean Sherk - Full Fight Video UFC 84
Matt Hughes vs. B J Penn 2 Fight Video UFC 63 | MMATKO Mixed Martial Arts Videos, MMA Videos, UFC Videos
Fight starts at the 14:30 minute mark. A great back and forth for the first 2 rounds, BJ overexerts himself in the 2nd and injures his ribs.
Classic: Matt Hughes Vs Frank Trigg UFC 52 fight Video
Speaking of bad reffing, Mario Yamasaki misses the accidental knee to the groin, but this is one of the fights that had me jumping out my seat.
I tried to find the Dan Henderson vs. Anderson Silva fight, but the one I had was incomplete.