You're going to get a lot of recommendations for SVS, Hsu and Velodyne. These are all great subs and you can't go wrong with any of them. To this list I would like to add the Outlaw Audio LFM-1. Your $579 gets you a 325 watt amp, 25 hz extension and drop-dead-gorgeous looks. If you google this unit you will get dozens of rave reviews and not a single negative one. It looks and sounds like a $1000 sub (no middle man). Definitely one of the best values out there.