Back in the day, I used to dabble in car audio as a hobby. As a result of this I built a few different variations of subwoofer enclosures. Coming across this DIY home theater subwoofer project gave me a feeling of déjà vu and the ideal solution to my home theater subwoofer dilemma.
In the middle of setting up a home theater right now, all of the wires are running through the walls and components hidden in a different room. Since nothing else is visible except the TV, I don't want to have to see the subwoofer either. This project by Darren Kuzma was able to put four 6.5 inch subwoofers in a 36" x 24" x 5" enclosure. The perfect size for sliding under your couch unnoticed...until the plane flies overhead in the movie and your couch starts to rumble.
See the full details and component list here to build your own.