If it's strictly for home theater and you don't have to worry about looks, check into the SVS cylinder subs, or ported HSU subs. This is coming from a sealed sub fan. The ported subs will give you more output per dollar.
I've used sealed subs from both SVS and HSU and they both offer great value and quality.
While I've not tried any of their offerings, Epik has some interesting products too.
Best of luck.