Magfloats clean glass and don't grow at all ; )
There are some algae eating sucker fish that don't grow too big, but for the most part "algae eaters" can be a bit unreliable. Most will come to prefer other food sources over the algae that may grow in the tank. Also, in a lot of tanks algae won't be a problem. If you don't keep the lights on too long or have the tank in direct sunlight, you might not have much algae at all. If you do, a scrub brush or a mag float will be a more reliable way to keep the algae off the glass. You could also think about getting some sort of snail. But remember, if you leave the algae cleanup to the animals in the tank, you won't necessarily have a tank free of algae. In my experience you are more likely to just have a few trails where the algae has been eaten away.
Once your tank has matured more, you could think about getting a small group of otos. They stay fairly small, but they need a mature tank that has lots of algae, because it can be pretty hard to get them to eat anything else, and they will often starve to death in a tank that doesn't have algae.