Theremin.info covers the theremin from many angles. It has historical information about the life of Leon Theremin, patents, schematics, reviews of early performances, reviews with famous performers, and information on building a theremin.
They have an active forum for theremin enthusiasts, and a gig guide for performers and listeners. A section on the theremin in film features reviews of classic movies from the theremin’s film heyday, including some 50’s and 60’s sci-fi and horror classics.