Let's face it, snails have a bad rap as pests and hitchhikers in our hobby. I recently "acquired" some ramshorn snails and I've been really impressed with their ability to graze on all types of algae. I swear they even ate the last bit of the BGA I was battling. I have about 200 of them in an ADA 90-P and they and 1 ottocinclus are the only algae eaters in the tank.
See the algae on the overflow? It was completely covered in that a week ago. If you've not kept them before they're worth another look.
