How about a evil cleric enhancement tree?
Forgotten realms do speak of Nasty handmaiden drow female clerics of Lolth that wield whips with serpents with a nasty bite.
Lets add variety to the usual heal and res clerics with a bit of spells specific to each deity perhaps? Just a few spells to set one cleric apart from another with a different faith?
Spider summons, poison damage spells for Lolth?