Subwoofer Options

I'm thinking about adding a subwoofer to the sound system in my Liberty. I've been researching my options and have come up with the following small and somewhat powerful subwoofers:

Sunfire Super Junior
9"x9"x9" Freq. Res. 22-100Hz 1500Watts
http://www.sunfire.com/images/produc...SUPERJRSUB.jpg

Velodyne SPL-800R
10.125"x10.375"x12.313" Freq. Res. 16-120Hz 1000Watts
http://www.velodyne.com/velodyne/pro...l_SPL-R-BG.jpg

Definitive Technology SuperCube III
10.25"x10.25"x10.25" Freq. Res. 16-200Hz 650 Watts
http://www.abtelectronics.com/images.../l_sciiibk.jpg


Morel SoundSub 9
20" round x 5" Freq. Res. 30-160Hz 100Watts
http://images.amazon.com/images/P/B0...CLZZZZZZZ_.jpg

That last one is interesting since it's only 5" deep and comes with a bracket that allows you to hang it on the wall.

All of the above are home-style subs. I haven't investigated the car stereo options yet since they need enclosures, etc.

Let me know if you've installed a sub and have any advice.