Just when we think we've seen it and heard it all before, every now and then we realize that we are still learning! One really can't argue how past technology will always pave the way for future technology. After all, we can't have a future without a past, can we? Without further ado, I bring to you 5 mind blogging electronic musical instruments young and old would want one in their collection:

Mellotron
The Mellotron is truly and really a piece of boggling engineering that was essentially an analog polyphonic sampler keyboard and the precursor to sampling. The Mellotron, quite literary, made the actual sounds of the orchestra, all thanks to hundreds of looped tapes fed to keys. On the right side of the keys, you had the lead instruments with a choice of 18 different ones, and on the left side of the keys you had rhythms and background samples. Here is a little preview of how the Mellotron sounds like:
Ondes Martenot
I first heard about the Ondes Martenot from Barry Grey who used this magical instrument in the production of the theme music for the UFO series in 1970. I can see why Mr Grey would have used the Ondes Martenot because of the ghostly and beautiful melodic lines one can create with this electronic musical instrument.

If you've never seen the Ondes Martenot up close, you would think it looks like a piano but actually the keys are not real. This 1930's electronic musical instrument basically produces a continuous variable pitch tone via a ribbon and white button. The sound produced is regulated via a volume potentiometer control made up of a small leather bag filled with carbon powder, which is quite peculiar since most potentiometers are either wire wound or carbon film.
SynthAxe
If you are a guitarist you may or may not know about the Synth Axe, which is easily one of the coolest-looking guitars I have ever seen! Only a few dozens of these were made in 1980's which explains why we probably haven't seen a SynthAxe before.
The SynthAxe is basically a MIDI controller/ guitar with a programming MIDI controller interface (can control up to 8 synthesizers) console and power supply pedal unit which are the electronics support system of the SynthAxe. The SynthAxe itself was made up of pressure sensitive keys and strings to trigger notes, as well as a 24 fret guitar neck with spaced out frets to get your fingers between them.

The Telharmonium
The Telharmonium is no doubt, the most mind-boggling electronic musical instruments on this list! I really wish I learnt about the Telharmonium in school since it's one of the first true synthesizer ever created. The Telharmonium dates from the early 1900's when amplifiers weren't yet around so this clever music instrument created sound by stacking sine ways on top of each other.

Reactable
A Ouija board springs to mind every time I tell people about the Reactable, but no, it's actually an electronic musical instrument with a tangible user interface that has been around for a good decade, yet you're probably wondering why you've never heard of it before.