I agree mostly with AJ. Yes a maroon or tomato clown. Maroon have spines on their chins they use to attack(hit) other fish to keep them out of the territory, it can be very harmful, but only if the fish keeps attacking the maroon. They will become overly aggressive if you put them in first because then the whole tank will the its territory rather then an area of 10"(they don't normally leave an 8" diameter from their chosen spot). Putting them both in at the same time would be best.
Now for the Triggers... I don't have too much knowledge, but I'd say get one that has a rating for a smaller tank like a Undulate Trigger and defenetly not a Clown Trigger. Also look for something that's going to stay less then 1' if possible like the Bursa Trigger only grow to be 9" and not 1' like the rest of them (accept for the Clown Trigger it can be up to 1'8") the small tank won't allow many territories in the future.
Good luck and post pics later!