Rumble vs the little asian dude
Tito vs Bader
Hendo vs Bisping
Wand vs Rampage 
Off the top of my head in no particular order:
Sell/Smith
Anderson/Belfort
Evans/Liddell
Wand/Rampage 2 & 3
Gonzaga/Crocop (Probably #1)
Etim/Barboza
Pettis/Lauzon
Yves/Berto
BJ/Uno
Bisping/Hendo
GSP/Hughes 2
Jardine/Wand
Carter/Serra
Nate/Maia
Weit/Lucarelli (This fight got me into the sport)
etc.
Kim Jong Uno -Agreed man I was in shock for quite a while on that one vtfuThatDudeButch - Nasty KO ever IMO was Gonzaga/Crocop. Basically sent him on the road to retirement. Brutal.
shit I forgot about this one. The twisted ankle, the open-eye KO and the fact that he died by the sword. What a fucking shock to my system that was.
Shogun KOing Machida back when Machida was deemed untouchable and unbeatable. 
Baroni/Menne
Vovchanchyn/Bueno
Daley/Smith
Powered by BALCO -
Scott Smith KO'ing Pete Sell was epic
this
Queue people naming the oldest KO they can think of. 'Cant be a noob' 'can't be a noob'
scourge -Oh this all day, couldn't have been choreographed any betterPowered by BALCO -
Scott Smith KO'ing Pete Sell was epic
this
Hendo vs Bisping was pretty awesome
Diaz vs Ruthless
*Wand on rampage - knees and falling/hanging on the ropes
* Hendo - Bisping
But their are many more but these 2 comes up as soon as i think about it..
Also Tank hitting that guy so he buckles against the cage was also ruthless.
Ah and Big Daddy elbowing the crucified guy...
Nsac/Trt
Trt was handily winning early on and through most of the match. Then out of nowhere nsac gained and unfair advantage by ruling trt illegal. Then commissions around the world all decided to jump into the fight on the side of the nsac. Turning the fight into a drama filled wwe stroyline.
Rizzo > Barnett. Awesome.
Condit vs Hardy. Throwing left hooks at the same time. Turnabout is fair play.
RalphHarris -This for sure.
Hendo vs bisping
You can't have a thread like this without machida
Machida-Evans
RJJH -Blue Flame Special -Rizzo > Barnett. Awesome.
You could see Barnett saying "Oh, fuck!" as Rizzo was lining up the second punch.
Barboza spinning heel kick