I bought the Wall Whale from Leslie's and I really like it. It's a nylon-bristle brush with a "fin" or "spoiler" that uses the force of the water to press the brush to the pool wall. It's a standard-size brush (18" or 21", not sure) that attaches to a telescoping pool pole. The fin can be removed and attached to a new brush when the original one wears out.
It's a little awkward to work with at first, but it's really great once you get used to it! Makes it a lot easier to give the pool walls a thorough brushing.