All right, I'll give this a go. I'm wording this as I am writing to a new fan. So don't get insluted if I'm explaining things you already know.
1. Dan Henderson vs Shogun Rua
One of the greatest fights in MMA history between two of the very best 205'ers of all time, displaying heart, mental toughness and a ridiculous willpower from both guys.
2. Forrest Griffin vs Stephan Bonnar I
The most important fight in UFC history and a scrap that stands the test of time. The aftermath with Dana announcing that both guys will get the contract and the fighters hugging it out is always a nice moment to see.
3. Anderson Silva vs Forrest Griffin
The greatest of all time at the very top of his game, absolutely dismantling the bigger, more physically imposing Griffin with Matrix esque moves. If this won't get you hooked on MMA nothing will.
4. Frankie Edgar vs Gray Maynard III
Everyone loves a good old Rocky story and it doesn't get much better then this. Frankie going on to scoring the KO on Gray Maynard after absorbing massive amounts of punishment early in the fight really is something to behold.
5. Don Frye vs Yoshihiro Takayama
To this day the craziest all out brawl in MMA history. Both guys threw technique out the window and went after each other like nothing we've ever seen before. This should get your blood boiling.
6. Chan Sung Jung vs Leonard Garcia I
A crazy slugfest of a fight that left Joe Rogan in the booth screaming "This is like a Rocky movie!!". A fight that will be rewatched again and again by fans in the years to come.
7. Fedor Emelianenko vs Kevin Randleman
In the legendary career of Emelianenko, this is a fight that really stands out from the rest. The way he survived the ridiculous impact of the suplex from Randleman and went on to win the fight is the stuff that legends are made of.
8. Anderson Silva vs Chael Sonnen
The injured Anderson Silva, seemingly down and out after the constant battering from Sonnen, pulls out a triangle choke in the dying seconds of the last round and gets the tap. One of those fights that couldn't have been scripted any better.
9. Nick Diaz vs Takanori Gomi
A fight that is often brought up when hardcore fans are discussing their favorite fight, and for good reason. A fight that had it all, exciting knockdowns, taunting, momentum shifts, and one of the most memorable submission victories of all time to end it all.
10. BJ Penn vs Diego Sanchez
In a fight many fans predicted Diego Sanchez would win by overpowering and outlasting Penn, "The Prodigy" showed the world that technique can overcome strength and power, and BJ won the fight by laser sharp counter punching and impeccable takedown defense, eventually stopping Sanchez in the last round.
11. Wanderlei Silva vs Rampage Jackson II
The second installment in one of MMA's most storied rivalries, Jackson was looking for revenge but was was left battered hanging in the ropes after taking a barrage of knees from Silva. The Axe Murderers finest hour.
12. Shogun Rua vs Antonio Rogerio Nogueira
In a fight where the winner would go on to reach to finals in the PRIDE Middleweight Tournament, both fighters laid it all on the line. A thrilling clash between two well rounded fighters who could do it all.
13. Antonio Rodrigo Nogueira vs Bob Sapp
A fight that really shows what BJJ and MMA is all about. After surviving the early onslaught from the much bigger Sapp, Nogueira eventually turns the tables and submits Sapp with an armbar.
14. Fedor Emelianenko vs Mirko Cro Cop
In one of the most anticipated fights in MMA history, the unbeaten champion Emelianenko took on the wrecking machine Cro Cop. After early success with jabs and body kicks by Cro Cop, Emelianenko was able to turn the tide and win the decision in a intense and historically important bout.
15. Chuck Liddell vs Wanderlei Silva
When Wanderlei Silva signed with the UFC in 2007, the fans demanded his first fight should be against long time 205 standout Chuck Liddell. In a fight that was voted the #2 best fight in UFC history, both fighters left it all in the octagon and it proved to be worth the wait.
16. Brock Lesnar vs Shane Carwin
In a heavily promoted heavyweight clash, Shane Carwin seemed to have the fight all but won in the first round, hammering the champion with strikes. Lesnar survived the storm and came back to win the fight in the second round with a arm-triangle, silencing doubts that he had no submission game.
17. Lyoto Machida vs Shogun Rua I
In one of the most stylistically interesting championship fights ever, karate expert Machida and muay thai fighter Shogun fought to a decision in a thrilling standup battle. Machida won a hotly contested decision, but the fight still stands as one of the greatest technical kickboxing bouts in MMA history.
18. Kazushi Sakuraba vs Royce Gracie I
In a grueling 90 minute battle without judges and time limits, the MMA poineer Royce Gracie suffered his first ever loss at the hands of Kazushi Sakuraba. Sakuraba would go on to beat several other Gracie clan members, earning him the nickname "The Gracie Hunter".
19. Chuck Liddell vs Tito Ortiz II
The long-awaited rematch for the belt would finally happen at UFC 66, after two and a half years of tension and trash talk since their last encounter. Liddell finished Ortiz by strikes in the third round, making his fourth title defense. The event scored a impressive 1 million PPV buys, and was a big success for the UFC.
20. Shogun Rua vs Jon Jones
Jon Jones was the challenger that awaited champion Shogun Rua, who came into this fight being out almost a full year with knee problems. Jones proved to be to much to handle for the champion, who went down in the third round to knees and punches, making young Jones the new UFC Champion of the world.
21. Diego Sanchez vs Clay Guida
The fans knew what they had coming their way after this fight was announced and it did not disappoint. Both guys swinging for the fences from bell to bell, tagging each other with hard shots but popped back up and kept going.
22. Georges St-Pierre vs John Fitch
GSP's title defense was expected to be a tough one, against the nard nosed grinder John Fitch. St-Pierre rose to the challenge, and battered Fitch for the entire duration of the bout. Fitch refused to get finished and hanged on for the whole fight, but he looked at no point likely to win the fight. St-Pierres best performance.
23. Ben Henderson vs Anthony Pettis
In the very last WEC fight, "Bendo" and "Showtime" left it all in the cage, providing some technical, high paced action. One of the most memorable moments in MMA history comes from this very fight, when Pettis landed one of the wildest kicks we have ever seen in the cage.
24. Nick Diaz vs Paul Daley
Two red hot rivals clashed for the Strikeforce Welterweight Championship, and fireworks ensued. Diaz seemed willing to slug it out standing with boxing standout Daley, and after getting dropped a few times in the opening minutes, Diaz turned up the pace and peppered Daley into a first round stoppage.
25. Randy Couture vs Tim Sylvia
For his return fight to the UFC, Couture would face 6'8 dominant heavyweight champion Tim Sylvia for the title. Not many people gave Randy much of a chance if he had to stand up with Syliva, but Couture, to a deafening roar of the crowd, dropped Sylvia within seconds of the first round, and went on to win every single round, thus becoming the UFC Heavyweight Champion at the age of 43.