This is something that Tribal brought up, and I don't know if its in the game yet, but how interested would you guys be in combos that require two classes to use them? The issue here is the AI, because it likely won't combo behind you, so you'll need to watch what abilities they're using and then tag yours to go off quickly.
An example, though, would be that grease spell followed by some kind of sneak or smite from the thief or fighter for extra damage or other results.