Theremin

Australian Theremin Kits
Simple kit. The completed instrument puts out a pure sine wave tone.
http://thereminkits.com/

PAiA Theremax
Information about theremin kit from PAiA.
http://www.paia.com/theremax.htm

Theremaniacs Theremin and Harmonic Percolators
Manufactures a pitch only Theremin with changeable timbre. Also presented is the Harmonic Percolator, a distortion pedal.
http://www.theremaniacs.com

Wavefront Technologies
Makers of both a traditional theremin and a portable model, and also a MIDI interface.
http://www.theremin.ws/