I would second the vote for Mirage. Their Omni S-10 or S-12 are a great choice and should be in the $500 to $750 range you mentionned. Paradigm's PS series are also heavy hitting subs although the bandpass design sometimes puts people off depending on their music preferences ..... HT performance is never an issue with those.

SVS (ie. 20-39 PCi) and HSU (ie. VTF-2 MK 2) both make amazing subs and have 30 day money back guarantees.

The lower priced Axiom subs, from what I've listened to, are a bit underachieving for the price. The new v2 of the EP-350 ($750)has been getting great reviews and of course the EP-500v2($1300) and 600v2($$$$$$) are reference units but also price themselves out of your range.

Audition what you can and let your ears decide. Good luck.

Shane