Vitor v John Hess.
Vitor used his head as a speed ball.
PablosNewton: I believe the other guy that Tank fought and KO'd against the cage was Steve "OH FUCK HE'S DEAD" Nelmark.
mark kerr vs Varelans. those knees were brutal.
mark kerr vs gurgel. those headbutts were brutal.
fedor vs nog. not being funny. i thought nog took a tremendous amount of abuse in that fight.
terrell vs lindland
trigg vs lawler in the corner
igor vs floyd webb?
igor vs goodridge 2
ricco vs fulton
riggs vs. alex steibling..most brutal thing i have ever seen. even though riggs got triangled to lose, if anyone has seen that fight, they will know what im talking about
me vs. teddy chapman in 3rd grade, mrs. ellisor's class....he stabbed me in the arm with a pencil after blacking both my eyes and smashing my nose....revenge was sweet though: i banged his girlfriend and then ko'd him in front of her when he confronted me in high school...>TAKE THAAT TEDDY
BM21
Gabe vs. that piece of ice cream cake
Matsui v Silva
Matsui v Belfort
Mats-... Ok, that's just mean.
Hess v Belfort
Coleman v Goes
enson - herring would have been another, but was stopped prematurely...
Arona punished Sakuraba pretty badly as well
Goodridge X Olag T
Igor X Bueno
Ortiz X Shamrock I
Frank X Ortiz
Ludwig X Shad Smith (Muy Thai Clinic)
enson/igor and fry/amrey tied for first place.. remember john asking "whats he saying" more, more i think hes saying more.. lol..
shad/ bang was horrible.
bart vale and that kid from john matuas school in the wcc. kapukuialua. thats fun
..." Bitteti vs Mestre Hulk TUF NOOBS! ;)"
Hey hey, keep it after 2004, huh Grandpa?! 
Speaking of newer fights...
Arlovski v. Justin Eilers, UFC 53. Eilers got worked in one round and left the fight with a broken nose, broken hand(I'd heard both hands were broken, actually) and badly torn ACL.
GSP vs. Mayhem
Silva vs. Sak 1 and 3
Tanner vs. Val Ignatov was pretty brutal.
There is also a fight clip from the MMA documentary "Rites of Passage" in which the ref is way too late to break the fighters. The kid that was getting pounded wakes up and starts mumbling/groaning. Pretty horrible.
Freeman smashing Mir
Some of my picks (the second one is from a local amateur fight here in Oregon - this guy sprayed me with blood).
It hasn't been mentioned and I dont know that it is the most brutal but I remember it being a good beating, Orlando Wiet ravaging Lucarelli. He beats him down walks away thinking he has won then relizes no one has stopped the fight despite the fact that his opponent is laying in a heap on the ground and RUNS back oven and gives some more mean elbows and knees.
Also Vitor using Hess' head as a basketball and dribbling it off of the ground with a pelethora of punches was brutal and well deserved.
The stiebling mention was a good one and I think Stiebling deserves serious props for showing heart beyond belief and not just surviving but some how pulling of the win.
For those who haven't seen it imagine if the Igor Enson fight would have continued another round, had a bucket of blood added to it and then Enson would have pulled off a triangle and won.