I know I'm going to ragged on for this, but f*** it.
I've always wanted to see Mirko Crocop vs Brock Lesnar. Why...cuz Mirko has no choice but to fight or probably die in the Octagon.
Rickson Gracie vs Bas Rutten
GSP vs Van Damme prime. Not joking he's got a very good kick boxing record and he's fighting again at the age of 50 in April of 2011. The man obviously has skills.
Anderson Silva vs Shogun
Demian Maia vs Robert Drysdale in an MMA setting
A young Pat Smith vs Pat Barry
A young Ken Shamrock vs Tito Ortiz
Fedor vs Brock
Prime Frank Shamrock vs GSP s Tito II (anybody have the link to Frank's fight against Tito.)
Finally I'm sure everyone would have loved to see Master Bruce Lee evolve his game and compete with the fighters of today. Hate the way people say he would not have done well. What about transporting in time and see if you could have beat him in the 60's or 70's without the knowledge of BJJ there is today. Look at what he was doing back then and compare to UFC in 93 or in the 90's. It's been 40 years man. He would have adapted his game and wrecked shop. Look at one of his best students, Dan Inosanto. He's got multiple black belts in various art forms. Imagine the master then.