Well, theres a few different options as far as Algae eaters go... Otocinclus are cool, and small. The only problems ive noticed with them are their sensitivity to water conditions, and the annoying hit or miss likelyhood of the fish to eat your algae. Some do, mine dont, who knows if they will or not?
For Hair algae, you cant beat a japanese algae eating shrimp, or amano shrimp.
There are also some breeds of Plecostomus that dont get more than 6 inches... Rubber lip and bristlenose are the most common that i know of.