Outlaw Audio subs are in the "best bang for buck" class, and I'm sure there are others.
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.
Edit: I was thinking HSU (but typed Outlaw Audio).......my mistake.
Of course as stated (and I've read it at other times), HSU makes the Outlaw Audio subs anyway.
I have no listening experience with Outlaw subs, but I have setup HSU subs in the past (I did like the results).
I use two VMPS passive subs in my system.