Bristlenose plecos are great for smooth types of algae, and get to about 5". Siamese agae eaters are great for hairy types of algae. They get to about 6", and should be kept more than one to a tank. Don't get Chinese algae eaters, they start to attack other fish as they get older.
Otos are good, and most fish will leave them alone, but if you're getting large, aggressive cichlids, they're not a good choice.