Steinberg Model E
Steinberg's Model E holds quite a significant claim to fame, for it was one of the very first commercially available VST plug-in instruments (Native Instruments' Pro-Five came out about the same time as we recall).
Now, more than 11 years after it made its debut, Steinberg has brought this synth back, and it's made it available for free.
Taking inspiration from the Minimoog, Model E is PC and Mac compatible, and there's even a 64-bit version. It comes as part of the VST Classics Vol 1 pack, which also contains the VB-1 virtual bass guitar.
You can download VST Classics Vol 1 on the Steinberg website. Note that this is an unsupported release, so if it doesn't work for you, you're on your own.