I just set one up in my 10gal. It's a Penguin, exactly like fishnutham described, complete with venturi air valve and sponge intake. It pumps 170gph which creates a strong current in that sized tank, but I have it angled to shoot down into a corner where the water then ricochets back accross the bottom of the tank and seems to work fine.
A cave is a good suggestion though. I have a couple large rocks which creates some calm spots. The calm spots are also where all of the uneaten food seems to collect which makes cleaning easy.