OM-1 Cassette Tape Synthesizer
File this one under utterly uniquely sounding analog synthesizer.
The Onde Magnétique OM-1 is a device with which you control a modified cassette-player. Into the player you put various pre-recorded cassettes (flute, vox etc) and by playing the buttons on the controller you set the speed of the cassette motor. Which in turn produces notes in different pitches. Really cool concept. Like the bastard child of a Mellotron. Check it out!
The OM-1 costs $285 and can be ordered from their web site.