As a young man I watched Pernell Whitaker vs Oscar De La Hoya like 500 times. I scored it round by round multiple times looking only at one fighter or the either. I counter every punch landed. 
I've seen Edgar Maynard 2 far too many times
YonYones - Aldo vs Swanson. It took me a minute but today alone I watched it 9 times
How did you watch an 8 second fight in a minute? You'd need at least 72 seconds... Just kidding, but I've always wondered how'd that fight would have been had Aldo not done that. What a killer Aldo was, he still would have won but we might have an all time classic. Frankly Cub is not what he once was anymore and the game has passed him.
PrettyBoy - As a young man I watched Pernell Whitaker vs Oscar De La Hoya like 500 times. I scored it round by round multiple times looking only at one fighter or the either. I counter every punch landed.VU for being the only other boxing answer so far.
Frye vs Takayama
Hagler vs Hearns
Balboa vs Creed
Snuka vs Piper
Off the top of my head...
Forrest vs. Shogun
Diaz vs. Daley
Lauzon vs. Miller
Travis Browne vs arlovski
Silva Stann 
Mel
Melendez v Sanchez is probably the most recent fight I watch regularly.
When ever people that come over are newish or a little inexperienced with UFC, it's Silva V Stann, or TKZ v Dustin. Two of my Favs
I've watched Lawler vs mcdonald 2 at least 100 times. The staredown after the end of the 4th round still gives me chills.
how many times did you guys watch the full Sylvia Emelianenko fight in gif form? I'd guess I saw it 200 times.
so that , Gomi Diaz, Silva Franklins, Diaz Lawler, Smith Morris.
Gatti-Ward
Nog v Herring 1. Stands up as a great heavyweight fight with high points for both guys. Back and forth the whole fight.
And as a kid from the Tyson era, would've seen Tyson v Holmes a bunch also.
OnceAndFutureKing -Haha I was going off 7 seconds but I agree with everything else you saidYonYones - Aldo vs Swanson. It took me a minute but today alone I watched it 9 times
How did you watch an 8 second fight in a minute? You'd need at least 72 seconds... Just kidding, but I've always wondered how'd that fight would have been had Aldo not done that. What a killer Aldo was, he still would have won but we might have an all time classic. Frankly Cub is not what he once was anymore and the game has passed him.
Arona-Wand 1
Igor-Varelans
Korean zombie vs Garcia probably, I don't usually rematch fight more than a couple of times
Hendo vs Shogun I
Hendo vs Wanderlei II
Fedor vs Cro Cop
Nick Diaz vs Gomi.