Well beyond the usual monster types, you could have them be like planewalkers. They aren't QUITE outsidered but they are infused with a particular plane, and thus their magic tends to have a basis in that. Example, a sorcerer who has blood ties to Hell would favor fire and lawful types of spells. So like a dragon, he could gain a divine spell to cast as an arcane spell, but ONLY from say Law and/or Evil. Or a Shadow sorcerer, cast only stuff with the Shadow descriptor.
Also they only can summon types native to their planes with summoning spells, if they pick one. And they tend to be able to sponatously cast plane walking type spells or spells related to their plane.
That help some Limp my friend?