If the temp is not too high, a weather loach is pretty cool.
You could also use something that would get rid of the future algae and keep the tank clean, like a snail (only one and watch for eggs), borneo sucker. A pleco could be cool too.
Also, dwarf frogs are interesting and do not get big. I would not mix snails with frogs however. I think mine ate away at my snail that was in perfect condition and ended up dying when put in with the frogs.
Neon rainbow fish are zippy pretty cool looking fish.
I have had all of these and still have them all except the pleco and the snail. My favorites out of them in order would be the borneo suckers, snail, then weather loach. Get a 2-5 borneo suckers for that size tank and that should work. I have 2 in my 20 gallon and I have yet to touch it with an algae pad in a years time or more. There are some very cool looking borneo suckers around and some bland ones, so be picky in picking some out if you went that route. They only get about an inch or so big.
Before you add anything, make sure they are compatible with your other fish. I am only recommending things I have had that I like. I do not know if they are compatible, but I would think most of them are.
I would stay away from shrimp, lobsters, fiddler crabs. They will all attack what they can. I have had a chameleon shrimp and a fiddler crab, so I do know they will go after other fish. Have fun choosing some fish.