HOB you could use a CPR Bak Pak. Good. Reliable. Should you upgrade will work on 32, 40, and 50 gallons. Can also later be used should you set up isolation or QT. I'm sure there are others but I've only used the Bak Pak on smaller tanks (10, 29 biocube, and 40 breeder).
Are you having troubles with your tank? We have a good thread in the nano forum on the subject on whether or not a skimmer is needed in a small tank. fwiw I pulled my skimmer about a year and a half ago and haven't looked back. I keep a mixed reef 29 gal. The reason I asked the question, is that, IMO, you should only add equipment to address an issue.
I'll see if I can link up the thread, as there are first hand recommendations on nano skimmers if you decide to go that route.