We are told there are only twelve models of humanoid Cylon. (there are also twelve colonial planets...is there a connection?) So far the Humanoid Cylons we have seen:
1) Six - white female (played by Tricia Helfer)
2) Sharon Valerii (Boomer) - Asian female (8) (played by Grace Park)
3) Aaron Doral - white male (5) (played by Matthew Bennett)
4) D'anna Biers - white female (3) (played by Lucy Lawless)
5) Leoben Conoy - white male (played by Callum Keith Rennie)
6) Simon - black male (played by Rick Worthy)
7) Brother Cavil - white male (played by Dean Stockwell)
Update 2/24/06: Sharon is apparently model 8. Biers apparently model 3.
Update 3/10/06: A new model of Cylon. Played by Dean Stockwell.