Etherwave Theremin

 The current standard Theremin instrument
The Moog Music Etherwave has rapidly become the definitive instrument for Theremin beginners, for good reason: it's solidly made and has excellent performance. Theremins are an inherently difficult insturment to begin with, and a poorly made instrument can easily make the difference between "incredibly difficult" and "completely impossible". Unlike most cheaper Theremins, the Etherwave is definitely playable, and professional musicians do use it both on stage and in the recording studio. It has a thick, solid wood shell, and two detachable chrome antennas which seem more solid in person than they do in a photo. The unit is relatively lightweight, and I'd guess it weighs about the same as my laptop.

As for its sound, it has a fairly classic theremin sound... some people complain it's a bit thin, but I've found that depends a lot more on the amplifier and (if applicable) equalizer used than on the instrument itself. When hooked up to professional gear, my Etherwave sounds rich and fat.

My Etherwave has appeared at several major science fiction conventions. I like that I can throw it in a small bag over my shoulder, pack a small amp in another bag, and use a standard microphone stand that's borrowable at most performance venues if I don't want to carry one. (I have a folding stand I can bring along, too.) Probably over a thousand people have toyed with my Etherwave, and most of them told me they had fun with it. The instrument's difficulty does not subtract from its fun value.

Don't forget that at a minimum you'll also need to get an amplifier (a keyboard amp: the Etherwave is a bit too powerful for a guitar amp although one can be used in a pinch), a stand (a microphone stand, as I said, without a boom arm), and an audio cable to connect the Theremin to the amp (a standard inexpensive "guitar cord" with 1/4 inch male connectors at both ends).