Snails definitely. When he says turbos there are lots of different kinds. For general eating get a couple astrea snails. Sometimes called turbos. For larger stringy substantial algae, ie hair algae, get mexican turbo snails. I woudln't buy more than 2 of them for your tank. They can eat themselves to death. Cerith and nassarius snails are good at going into the sand and helping stir it up. I have mini strombus snails in my 12 and 20 that are great at handleing the cyano and diatoms on my glass. Not to mention they reproduce in my tanks. I have babies everywhere. I have heard conches also do a job on cyano and diatoms but im not sure on that one. They are so expensive sometimes i don't bother. A small queen conch around here is 10+ dollars.... Hermits dont hurt either in keeping things clean so the cyano and diatoms don't have a food source....
EDIT: the strombus are not buyable, i may change that one day
, but look for them at the LFS about 30 minutes before they close. They come out more at night.