I've got four of the "standard" Bass Shakers from Aura (via Parts Express) under the front sofa in Bogie's Bunker. When the dinosaur stomps, you feel it.

I recommend running with a plate amp with volume/xover controls - a full range amp will send too much music, and some DVDs just won't work. I also run one side of my Behringer Feedback Destroyer to my subs' amps, and the other side to the shakers' amp, with different EQ/cuts.