So what sub are you using for your Home theater?

I use 3 Vandersteen subs. 2 - 2Wq for the front speakers, 1 - V2W for HT and located in the back of the room. My system is used 50/50. Same comments as SDCAMPBELL about Vandersteen.

I guess it depends on how big your HT is.
My AV room is 12ft x 26ft. kinda a Big long hallway.

I use a Definitive Technologies ProSub 200. Its only 250W rms, but it shakes the hell outta my HT when needed. Good dispersion, and pounds out some very good concussion. I honestly cannot see any reason to get something bigger than this unless my listening room gets alot bigger or i feel like cracking my foundation.
In the beginning of "Attack of the clones" when the luxury liner escorted by fighters flys overhead, it gave enough power to rattle a glass off my coffee table. Its not "Too picky" about placement either.

Works great with music too. Gives great impact, very tight control and doesent sound too boomy.

Ive auditioned Subwoofers from Infinity & Velodyne that cost quite a bit more and still, IMHO believe the ProSub 200 outperformed them in many ways. If there is a local "SoundTrack" audio store, you can check these out there. They also carry the Sunfire brands as well as several others.

MSRP $549.00 So it doesent break your wallet

Sunfire True Sub.

It works, but even with a "cheater plug" it puts out a hummmmm. I only use it with movies (nice!!!), so its un-plugged most of the time.

I use an ACI Titan II for my home theater.

I started my HT system with 2 cheapo Velodyne CT-80 under both endtables on two sides of the couch, extremely happy with that setup. Not only did it rattle everything, but it also "vibrates" my clothes and goose bumps....
Then I thought it even gets better if I upgrade ... you know what I mean.
So out the CT-80s and in pair of HSU VTF-2s, believe it or not, I missed the CT-80s right from first 30 minutes.
Then out the VTF-2s, and in a pair of servo controlled Velodyne F1200, still nothing like the CT-80s.

Only problem of CT-80s is music, even though I have SPL-1000 just for music, but my task is not done yet.