Totem Acoustic Beak
Erick Lichte mentioned Totem Acoustic's Beak, which costs $125/pair, in his follow-up review of the Totem Forest loudspeaker in January 2010. The Beak is a bullet-shaped device, about 2" high by 1.5" in diameter, that's intended to be placed atop a speaker to control "parasitic resonances." I was given a pair of these more than 10 years ago, and have tried them with various speakers. While Erick didn't find the Beaks to make any difference to the sound of the Forests or any of the other speakers he had to hand, my experience was different.
VPI Magic Brick
The VPI Magic Brick is an 8lb block of steel laminations, about 5" by 3" by 2", encased in a nicely-finished oak box for aesthetic appeal and for protecting whatever the brick is sitting on from scratches. Placing the Brick over the power transformer of a piece of electronic gear is supposed to improve the sound of your stereo system.