Whilst I was posting the last youtube clip of the monome I started looking around for a free VST granular synth... there's a few but not as many as you'd think. An oldie but a goodie is Grainz from SKnote. You can click the image to get a better look. You can have a listen to demo HERE.
Grainz will bend, twist and generally fubar your audio beyond all recognition in a handy VST format.
A more rhythmic option is Minerva from Tweakbench. Probably the most capable granular synth I've ever used is the shareware Crusher X Live. I really enjoy the morph function, it can sound fantastic morphing from one patch to another. I never had a chance to use the multiple speaker outs to get the true vapour/cloud synthesis effect but that is going to change. In a few weeks I'll have use of a lovely 5.1 monitoring set-up and Crusher X is going to be put through it's paces :)