I'm sure you know
http://www.kvraudio.com/
I'd say anything by dfx or their affiliates is worth getting.
Any granulizing VST, especially KTGranulizer.
DBlue Glitch is cool, if you use it subtlely!
Can't remember who did them, but the team who did GLITCH GIRL, GLITCH JOCKEY, etc. just flat out rules. The sickest, weirdest vst plugins ever.
These all rule:
http://www.remixsoft.com/plugins/wei...st-instrument/
As far as "keys", I always loved String Theory.
I will download a VST plugin and use it exclusively for a bit, checking the ins and outs of it and how it can be manipulated and for what purpose. Any VST in combination with a pitchshifter (and perhaps an equalizer, especially any kind of dynamic eq -- you know, sounds swirling around) can be a good ambient effect, even if it's just for some strange noises in the background.
I dunno. If you ask for something more specific, maybe I can be too. Not too sure about VST synths, I just usually go for the ones that replicate real synths, like moogs, and go from there. Those aren't free but are easy to find on torrents/slsk/etc.
Just explore the kvraudio boards and shit, you'll find what you're looking for.
Really, it's harder to find VST's NOT worth reccomending.
As far as Robe. goes, we don't use many VST's, as we just line in our stuff, maybe mess with some compression and equalization but that's about it. But for Scissor Shock, I've used hundreds of VST's. KTGranulator is my absolute favorite for getting just really really bizarre sounds. I also like to use the FUZZ BOX vst plugin, gets an almost Albini like tone..
Get DirtBag (organ synth vst) from here:
http://www.spacenoah.com/musicsoftwa...nstruments.htm
I dunno, just too many to name, I have thousands on my various computer.