In 1919 a Russian physicist named Lev Sergeivitch Termen invented a radical instrument that is played without touching it. The user moves her hands around two antennas to control pitch and volume. The result is an eerie, sci-fi sound that has been used in music as well as spooky movies of the 50s and 60s like "The Day the Earth Stood Still" and "It Came From Outer Space".
Even though most people have never heard of a Theremin, everyone has heard the sound many times. This playlist contains songs that feature this whacked-out instrument.
The most well-known Theremin riff is probably found in the chorus of the Beach Boys "Good Vibrations" so listen closely. The Beach Boys used an "Electro-Theremin" as opposed to a traditional two antenna Theremin, but the sound is the same so I have included it here.
Please note that that Theremin is used in many more songs than are listed here, but this 30 song playlist will give you a great well-rounded view of what can be done with the instrument.