Oceanic makes a nano skimmer, I bought one for my little 10 gallon. It works ok I guess, ive had to replace the air "stone" about once a month just to keep it working ok, its a wooden air block, and it kinda starts rotting out. I tried an actual stone, but it didn't produce the needed bubble action.
I just purchase an Aqua C Remora Nano for my 18 gallon. It's been running for a couple of days on an empty tank, just to get the break in over with, but so far its noisy as heck, which they say stops after its broken in. Not sure yet if it skimming capabilities are worth a crap as its running in new water with no bio-load for now.....come to think of it, I don't know if the break-in will even start without a bio-load...dang it.