I thought you guys would not only find this interesting, but have the knowledge to follow through with it. I made a pair of them a bunch of years ago using Pioneer 12" subs and an old 70W x 2 Technics receiver. It made the door on my oven downstairs rattle (I had only a 150W, 10" powered sub, so that was not what was shaking anything)
http://www.hometheaterhifi.com/volume_4_2/tactile.html
Tips: Use loctite on the fasteners, ensure you can add/subtract weight to/from the bridge across the dustcap in order to tune it, and frame the fukers like you mean it. You will NOT be dissapointed. It REALLY added to the HT experience, unlike anything I've heard/felt before. Commercially available "shakers" tickle your bum compared to these.
*Caveat- I used speaker-level outputs from my main HT receiver and converted those to RCA level inputs for the shaker receiver, often putting 9V of input into that poor thing. It lasted a year, but could easily be reproduced with a good plate amp meant for HT subs.