People who are too "obvious" to be Cylons:

Adama
Roslin
Baltar
Kara

My own guess:
Gaeda
Zarek

I was reading an interesting theory someone had about the final 5 cylons. So we're told that the final 5 are distinctly DIFFERENT from the rest of the human model cylons. The theory suggested that maybe the difference comes from the way in which the consciousness of the cylons is transferred. For the rest of the cylons, once they die, their consciousness is sent to a new body in the resurrection ship. We know that the ressurrection ships do NOT have bodies ready for the final 5, because the other cylons don't even know who the final 5 are. So maybe, the final 5 have the ability to transfer their consciousness into actual human beings. So the humans into which their thoughts are transfered into are acting as host bodies. They are in fact human, and their human history and background is real, but once activated, the cylon consciousness starts coming through.

I love this theory because it explains how someone as old as Tigh can be a Cylon and someone as random as Anders.

Do I think this theory is likely to be true? Nah. I think it's a bit too elaborate. Something that springs from the mind of an obsessed, crazy analytical fan, not a writer for the show.

It's fascinating to think about though.