Phyzmod is a free hybrid synthesizer VST instrument merging a Karpus-Strong generator and a classic substractive architecture.
Erzatz is a free VST somewhere between a vocoder and a pitch shifter, Ersatz is a simple effect splitting the signal up to 32 bands and re-generate it as a sinus stack.
GeekTronic is a free stereo bit-crusher / decimator VST effect plugin. Simple, efficient.
FreeFall is a free hybrid delay effect and pitch shifter VST Plugin.
Uniwave is a free VST synthesizer instrument based on a substractive architecture, Uniwave have also some FM capababilities. A few unusual controls permiting to tweak and bend your own sound.