Outlaw offers a money-back guarantee, as any company should that does not offer an opportunity to listen. I recommend heading over to Outlawaudio.com, registering in their forum, and asking questions in their sub-related threads after narrowing your search to some of their models. $800 buys a really nice sub. And the folks over there are very mature, very knowledgeable (see member Gonk for one of the best forum personalities around with questions - he'll respond to every thread if he has feedback).
My two subs that fall into that range are the Supernova (MSRP is much higher but retail you can easily get one in the $500-800 range) and the B&W - I bought the ASW650 from hifi house for about $600 and that sub also rocks. I love B&W speakers.