Royce tapping out Severn.
Royce beating Severn made me realize not just how good he was, but how tough he was. I've wrestled against Severn and back then he was as strong as bull, tenacious as a lion. I realize he never trained strikes or subs at the time, but to me that's the victory the legitimized Royce.
The first time I saw Royce choke somebody. Forget the exact fight (I watched 1-3 or 1-2 all at the same time). I was like --that's-- how a real martial arts fight ends, gtfo. Then he kept doing it.
2nd is Andy v Vitor. Hype train was huge. He, in his prime, jukes out the most dangerous mfer in the UFC, and kicks him in the fucking grill. Legend. 
Being in my living room watching forest vs Stephan TUF 1. I was watching and losing my shit as these guys were just winging it. Then the reaction Bonnar had when the winner was announced. It made me a fan.
Silva putting his foot into the face of vitor was the first event I watched with my wife. She lives silva now.
Ronda armbar on Tate in strikeforce and winning the title.
Hughes Newton finish
Belfort Silva
Hughes GSP armbar
Conor Aldo KO was crazy
Diaz McGregor
Fedor/Cro Cop stare down. Still get heart palpitations to this day watching this.
Gotta be either Robbie vs Rory or Hendo vs Shogun for me. Those were fights for the ages right there! Ten years from now I'm sure I'll still be telling new fight fans about those scraps.
Lawlor losing to hendrix, winning 3 fights in the next year, and then winning the belt was fucking amazing.
Biggest moments that come up whenever I talk about MMA would be: Wanderlei Stann fight, Silva leg break, BJ getting that welterweight belt. 
frank tapping tito was major shit at the time
Being there live for Wanderlei vs Chuck.
Diaz vs Gomi!!!
Fedor getting dropped on his head then subbing Kevin
Andy getting ko'd
Weird one but for me:
Anderson Silva vs Chael Sonnen I
GSP vs Hughes II for the high
Silva vs Franklin for the low
Frederick Ettish - Rhodes - Ettish definitely the most memorable for me, except that I actually don't remember a large part of it. They say head trauma will do that.VU!
I'm going to say Sakuraba vs Royce and then later Igor in the same night. Such a great story to tell new MMA fans.
I don't know about a particular moment, but the first MMA card I ever watched was Pride 33, fucking fantastic event, all finishes.
I was fucking baffled and hooked.
Vitor knocking out Wanderlei. I remember finding that clip on Napster back in the day. Before that I was mostly watching K1. That clip got me hooked on MMA ever since.
UFC 51. Pulling Evan out of a trash can less than a month before he won the title. Also, Paul's UFC debut was that night as well.
Anderson tapping Chael last minute or when I nearly broke my ankle and shredded all my ligaments jumping in the air and landing awkwardly drunk while celebrating a huge win, where I bet on Gonzaga to beat Crocop, because I had an actual dream that Gonzaga won.
Randy dropping big Tim at beginning of round 1
So many.
Don Fry vs Takiyama
Shinya Aoki vs Hirota when Aoki breaks his arm then flips him the bird while Hirota is rolling in pain.
Chuck vs Wanderalia years coming. Awesome scrap.
Wanderalia vs Vitor
And
Serra over GSP was literally jaw dropping for me