Well I think it goes w/o saying that bugs in general... as many kinds as you can get, are pretty important in any mix. Bristle worms do a great job of mopping up excess food, excrement and other larger sized pieces of stuff. I've found the Mini-Brittle Stars to be a great addition to. Stomatella's are one of the best type of film algae grazers... and they reproduce in captivity. I've also had good luck with Chiton's.
I tend to like Turbo's, Astrea's, Nassarius, and strombus snails. The Fighting Conch's I've only had recently, but think they are reef safe. I would only get a couple of them however, even for a large tank (90 gal).
- Mac