Goodridge vs yatsu was a great answer. Abyobe who hasnt seen it go watch, how that dude is alive I dont know 
Bisping vs Mayhem
GSP v. Fitch, Hardy, Serra II, Penn II, etc.
Enson v. Igor is the obligatory answer in these types of threads.
I will agree with the chappie who mentioned Lauzon vs. Michael Johnson, a recent fight that sticks in my mind as tough for me to watch.
Speaking of Creepy Joe, I know it didn't go a full round, but damn the ass whooping he put on Gabe Reudiger in Boston.
Randy vs. Tito... It was great!
Arona v Sakuraba 
me101 -This toogarrote - Vovchanchyn/enson
This, total domination by vov and superhuman heart from Enson.
One of the most brutal fights in MMA
Fedor vs Goodridge
Belfort vs Henderson.
jhedges - Forrest Petz v Sammy Morgan. There was something like 7 or 8 knockdowns and really the fight should have been stopped a couple minutes into the first round. Somehow, it made it to a decision where one judge scored it 30-23 (others were 30-26 and 30-27 WTF?).Was gonna post this. The meat cleaver! Loved watching Petz fight
Matt Wiman vs Cole Miller more one sided than I'd expected
ando vs bonnar and griffin are a good example. its not a 1 second ko, but a domination in every aspect, toying with them, and a finish as soon as he feels like it
The beating Cabbage took against both Arlovski and Timmeh were both hard to watch.
He was a human punching bag in those fights.
ImaLilFruitCup - It may have only lasted a minute or so.. but I still cant get over Joe's beatdown of Gabe a couple years ago
This. The most one sided beatdown in ufc history in my opinion.
I was about to say GSP Serra II, but then I remembered Cain JDS II.. Holy fucking shit!
DragonDidn'tDrinkEnoughPee - Hettes vs nam pham was very one sided, think it was a prelim so I dont know how many watched it but he basically beat the shit out of him on the ground.VTFU for that reminder
Just checked judges had it
30-25
30-26
30-25
Andy - Maia. Anderson was playing around with a child
Jimmy hettis vs nam pham
shogun rampage was the first to come to mind
Shields vs. Henderson. I remember thinking that fight looked like a "Gracies in Action" video. Hard to fathom how one-sided that was.
My fave was bj vs Diego. Just a massacre.
I also remember thinking rich franklin was such a badass when u just made Edwin dewees look like a child. That may have ended in first round tho