Richard Taylor sampled various sounds from something like twenty synths and placed the samples in the Public Domain. These aren't actual synths like something made in Reaktor. They are basically presets that you can mess with using various effects. As usual on electric type instruments, I used Mickaël Ménager's great Kontakt script and GUI.
On my first attempt I just dropped the samples in and made the instruments. There really was too much dead space in front of the samples, so I went back and used Audacity to tighten things up. This version should be much more responsive. Also these generally use standard wave files, so if you don't have Kontakt or just want to use them that way you can.
I really don't understand synths as I more of an acoustic guy, so I don't know how useful these instruments are. I had fun just messing about with them and there are some pretty neat sounds. Again these aren't true synths, but multi-samples of synth presets.
Bender Roma Equator (Thanks Fleer)
King 1 Many Part 1 Part 2
Newtron V Part 1 Part 2