What type of algae? Different fish will eat certain types, some types will not be eaten by any fish.
If you're considering just a basic fish to deal with common green algae on plant leaves, there are several species. Oto catfish, Farlowella vitatta, Bristlenose Pleco, plus some other fish like molly, headstander, some of the barbs, etc. Click shaded names for the respective profile.
Brush algae is another matter, and there are two fish that will eat this, one I can't remember and the other is the Siamese Algae Eater that Granberry mentioned. Check out their profile though, you may or may not want them.
I would never get any fish solely to deal with algae; the entire community has to be considered. If you like these species as fish, fine; the algae issue is a bonus.