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.