1) A Thieve\'s Guild would be one of few guilds that are actually guilds, so that\'s always good. Especially WARRING thieves guilds.. bwahaha. Note, however, the concept of a rogue\'s guild is like saying \'organized anarchy\'. You\'re not a rogue if you\'re part of a group, you\'re a rogue -group-, perhaps, but individuals, no.
2) Cults are good. Especially ones that are very sure they\'re the good guys.
3) Has nobody thought of spellcasters yet? Necromancers? Enchanters? Evil bards? Evil bards are always fun. Indeed, my bard is somewhat of that nature.