Something like the Onix Rocket UFW-10 should work just fine. Get one new from here AV123. You don't want to over load the room. A sealed 10 inch should be more than enough.
Subwoofer reccomendations
I am looking for a subwoofer to go with my Sonus Faber Concerto Stand mount speakers. It must be quick and musical because I don't want to lose that Sonus Faber midrange to a black boomy box in the corner. My two choices for now are a REL storm III, or a martin Logan Depth. I may even go down to a REL strata III. My room is on the small side, about 14 by 12. You can see the rest of my system on Audiogon. I'd rather not spend more than $1200 on a sub new or used. I have heard the Storm III before, but it was in a VERY large room, and it didn't have enough for the room size. I have never heard the Depth before. Please help.