I own the Red Sea Prizm skimmer for my 18 gallon. I would look in to the back pack though. I've also heard good recommendations on it.
Another one you could look in to is the Aqua C Remora HOB protein skimmer, it is slightly different from the rest of the skimmers because it uses a different method of skimming and from what I've read about it it is pretty quiet. The pricings are around 150 to 170.