What extra roles have you used with Werewolves?
I've played with several of the roles invented by The Graduate Mafia Brotherhood of Princeton University, but the most memorable was the Kingmaker:

A despotic regime has siezed power, usurping democracy. Each turn, there will be a King or Queen who has the sole power to decide who will be lynched. Open debate is allowed, but the day ends as soon as the King/Queen makes his/her choice.
The Kingmaker is a civilian, who, each night, names a King/Queen for the following round. The Kingmaker cannot choose himself, and he cannot choose the same person for two consecutive rounds. The Kingmaker must choose someone.

One game in particular, the Kingmaker's pleas of &quot;Don't bite the hand that feeds you&quot; went entirely unheeded.  We played the rest of that game democratically.
I also noticed that with too many roles in use, moderation can get ridiculously hard.