particle density volumetric material
I made a volumetric material in cycles based on particle density. The particle set I used is influenced by a turbulence force field. I used a small ico-sphere as a particle object and added an emission shader. I noticed a pretty noticable offset between the particles and the volume material that changes over time - I'm not sure yet where that offset comes from, but I think it still looks pretty.
you can download the blend file here
See also:
hard edge displacement
volumetric density texture
underwater particles
torus density texture