for my money, the asw 100 from monitor audio on sale at saturdayaudio.com. it's small but packs a decent punch and sounds very clean for its price. you will get the best from it in a small room.
In fact I know there are articles out there both in print and in forums about car subs just don't cut in the home theater. Something about design and drivers used makes it two completely different animals. What your room size and budget? I would say there are soem pretty good recommendations already listed.