To add to the posts of mc and Duke, make a GR Research sub or four. Rythmik sells the F12G as a factory finished model, and GRR sells it as a DIY kit. The kit includes the Rythmik A370 plate amp and a 12" woofer, which are used together in a servo-feedback system.
The Rythmik F12 has a 1.5cu.ft. enclosure, but the woofer may be used in an enclosure of up to 2cu.ft, which provides slightly higher output. Build the enclosure in any proportions you desire, and finish any way you like. Building it yourself, you can brace the h*ll out of it (take a look at how Jim Salk braces the enclosure he makes for the F12), and even use two layers of MDF or Baltic Birch ply (better yet, one of each), with constrained-later damping between the two. Dead as a doornail!
If you aren't interested in building an enclosure, Parts Express sells some real good sub enclosures as knock-down flat packs, very easy to assemble, wood glue and a few clamps (or even masking tape) the only tools required.