You will get a lot of suggestions but, don't overlook the Premiere Acoustic PA 150 it is one on my favorite subs that I have owed. It has good build quality and a beautiful finish. Great bang for the buck, I have owned several Klipsch, Epik, SVS and Chase subs to name a few. This sub has a decent low end and great mid bass slam. The Klipsch $299 subs are also a nice purchase.
Klipsch RF 7 based HT 7.4, Pioneer SC 35, Acurus 200 Five, Dayton 18 Ultimxa Dual Sub Cab(2), Dayton 18 Ultimax Large Vented Sub Cab (2), on Berhinger I Nuke DPS amps, Samsung BDP F 7500, Asus/My Book Live HPC 4 TB
Yaquin VK 2100 amp, McIntosh XR 5 speakers, Samsung BDP F 7500