I was thinking pick a few, then surprise us with 'em, hence the 'vote on them' idea wouldn't work. You can refer to the MS wiki for a list of roles, but common ones are:
Vigilante: Pro-town, can kill one player of his choice per night.
Serial killer: Independent of town and mafia, kills once per night, wins if he's the only one left alive.
Roleblocker: Can choose one person per night, whatever they were planning to do that night doesn't work.
Masons: two or more town players who can communicate at night, a la mafia.
Godfather: Mafioso who shows up innocent to cop investigations.
You have to be careful how you balance such roles though: don't add too many. I think a twelve-man game is best if we're using roles other than townie, mafioso, doc and cop.