Updated for Alien, Turncoat, Deputy, Informer and Snoop.

No warlock, baker, blue, 'nilla, leader, samurai, naive or paranoid cop, Cthulhu, enforcer, or shrink.

My reasons:
*Warlock and Baker tend to end games early for no real reason.
*Nobody wants to be a Blue, 'Nilla, Leader, or Samurai.
*Once they've found their sanity, Naive and Paranoid cops are essentially blues.
*Similarly, Enforcer and Shrink are functionally 'nillas/blues if there is no converting role.
*Cthulhu is screwed if there's no Cult, and anyways once someone goes crazy they'll just spell the Cthulhu's name in caps, outing him/her.