I can second (or third, or whatever) the SVS recommendation. I recently purchased their PC-Ultra sub and am quite happy with it. The built-in parametric EQ helps to tame a rather large 30Hz peak in my listening room. I was also surprised to find a SVS hat, pen, and T-shirt in my subwoofer box, in addition to the rather large cylindar.
Apparently, these guys know what they are doing, as well. I asked some rather technical questions relating to various components that I was planning to use with the sub, and they addressed them quite handily.
I've read rave reviews on their less expensive subs, too, but have not heard any of them. Going on the many reviews - both professional and blog - I doubt you can beat SVS for the price.
On a personal note, I feel rather odd promoting SVS subs on the Axiom forum. From what I've read, the Axiom subs do a bang-up job for the price, as well. Having no personal experience with them, I can't really comment beyond that.
