Thanks for the responses. As for room area/size, the biggest problem I have at the moment is that I'm planning on moving in the next few months. Into what, house or apartment, I don't know yet. So, I have no idea on room sizes.
Right now, though, I'm in a loft space with a ceiling that angles up from 9 ft to about 20 ft. The living/dining room area is open with concrete floors, is something like 17 x 15 ft or thereabouts. The sub I have now is an old 8" unpowered Sennet (Sonnett???) (forget the model # and not home at the moment to check). It's surprisingly good for something I paid $100 for 15 years ago.
I'm looking for a good sub that not only passes the wife test (not terribly big and ugly), but is musical with good slam and can handle a wide range of music genres with aplomb. If I had the money, and my wife didn't mind a sub/coffee table I'd go with something from Rel's reference line.
I'll check out SVS and HSU. And, before I forget, as for price range, I'm somewhat open and willing to spend in the $1000 range for a good, solid sub. Spending less, of course, would be better.