Tunze Nano 9002
Best little skimmer EVER!!!
I think I posted a thread on here somewhere about it. It has great reviews. The price isn't exactly cheap, but it's still cheaper than a lot of other small ones. (Rated for 26-52 gallons, not sure what yours is.)
I believe there are a few Remoras out there that are rated for even smaller tanks, but I'm not sure of the reviews on them. Regardless, Remoras generally seem to have positive reviews.