This blog is purely my opinion on the top ten rankings for MMA, but if you want other opinion's you can check out these: http://www.mmaweekly.com/topten.asp & http://www.sherdog.com/news/rankings/list

Heavyweight (206-265lbs):
1. Fedor "The Last Emperor" Emelianenko
2. Brock Lesnar
3. Frank Mir
4. Antonio Rodrigo "Minotauro" Nogueira
5. "The Baby Faced Assassin" Josh Barnett
6. Junior "Cigano" Dos Santos 
7. Shane Carwin
8. Alistair "Demolition Man" Overeem
9. Cain Velasquez
10. Brett Rogers

Light Heavyweight (186-205lbs):
1. Lyoto "The Dragon" Machida
2. Mauricio "Shogun" Rua 
3. Quinton "Rampage" Jackson 
4. "Sugar" Rashad Evans
5. Anderson Silva
6. Forrest Griffin 
7. Antonio Rogerio "Minotaouro" Noguiera
8. Thiago Silva
9. Luis Arthur Cane
10. Gerard Mousasi

Middleweight (171-185lbs):
1. Anderson "The Spider" Silva
2. "Dangerous" Dan Henderson
3. Nate "The Great" Marquardt
4. Vitor "The Phenom" Belfort 
5. Damian Maia
6. Chael Sonnen
7. Yushin "Thunder" Okami  
8. Jake Shields
9. Mamed Khalidov
10. Jorge Santiago

Welterweight (156-170lbs):
1. Georges "Rush" St. Pierre
2. Jon Fitch
3. Thiago "Pitbull" Alves
4. Dan Hardy
5. Mike "Quick" Swick
6. Paulo Thiago
7. Josh Koscheck
8. Paul "Semtex" Daley
9. Martin "Hitman" Kampmann 
10. Carlos "The Natural Born Killer" Condit 

Lightweight (146-155lbs):
1. BJ "The Prodigy" Penn
2. Shinya "Tobikan Judan" Aoki 
3. Eddie Alvarez
4. Kenny "KenFlo" Florian
5. Gray Maynard
6. Frankie Edgar
7. Sean Muscle Shark" Sherk
8. Diego "Nightmare" Sanchez
9. Joachim "Hellboy" Hansen
10. Gilbert "El Nino" Melendez
  
Pound for Pound (P4P):
1. Fedor Emelianenko
2. Georges St. Pierre
3. Anderson Silva
4. Lyoto Machida
5. BJ Penn

http://www.sherdog.com/news/rankings/sherdogcoms-pound-for-pound-top-10-16997