Check out the Mirage BPS-400 sub. (2) 12 inch active radiators with a 400 watt amp. It list for $1300, but Tweeter is selling them for $799. I only use mine for HT applications, but it does 'rock the house' very impressively.
What to look for in a sub?
I've been pretty happy with my HT setup using a Yamaha RX-V1, a mix set of speakers from Definitive, Paradigm, Acoustic Research, and a really old Fosgate subwoofer. (Most of the fund goes to the 2-channel audio setup) I am moving to a new house with a smaller living room, and the sub is too big. (30"W x 30"L x 15" H) I need to find a replacement sub that will fit into the new living room. What criteria should I look for in a sub? Also any suggestions for a good sub (new or used) in the $800 range would be greatly appreciated, active or passive. (I currently have a Marantz 50w monoblock driving the Fosgate).