I think Fassbender would make a great Bond, my only concern would be that in some films his accent is somewhat inconcistent. In Centurian half the time he was very English, but the other half of the time he slipped into his (natural I believe) Irish.
Bettany I can't see as Bond, Toby Stephens I'd love to be Bond, the amusement of a Bond villain playing Bond would be worth it alone. And of course he already has played Bond on the radio.
I like the idea of Bale, but he's Batman, and to be honest he's gotta make me forget T4 before I champion him for something like Bond.