Mexican turbo snails in particular for red turf algae, and then in particular this urchin:
http://www.liveaquaria.com/diversden...+4&ddid=107060
"Green Spined Pincushion Urchin (Salmacis sphaeroides)"
I have had two of these for the better part of the last 5 years or so and they have been hands-down the best rock cleaning service out of any grazer I've ever had. I've tried several other urchin species, none comes close to these guys. The caveat is that they're quite hard to obtain for some reason, at least around here.