The Theremin and the Ondes Martenot are still in use today - indeed the latter includes Radiohead's Jonny Greenwood amongst its players.
The Trautonium, a contemporary of these early electronic instruments, is less well-known today, but Paul Hindemith wrote for it in the early 1930s.
Related Links:
Trautoniks - custom-made Trautoniums and controllers.
Trautonium player Oskar Sala in 1941 ...and in 1991.
Peter Pichler plays Hindemith on the Mixturtrautonium.