This is a short demo video of things to come for Blender. If everything works out all right, volume rendering will be included in Blender 2.70 (hey, we don't even have version 2.69 yet).
As you see, under the right conditions like in the intro video the volume rendering is pretty powerful already, I got a basically clear render with just 200 samples. The second video shows an example where it fails at the moment. I used 1.000 samples and still lots of noise and hardly visible volume effects. That might have been the case because I used so many emitting surfaces for that demo video. For rendering I used a homogeneous volume for the world settings and 0 scattering bounces.
The volume code is at the moment in the Google Summer of Code 2013 branch by Thomas Dinges. If you want to compile it yourself, you can find the code over there. Some people made custom builds for various platforms. Check Graphicall.org and search for DingTo.