Now available for purchase at core-cg.com, Mental Core is a great re-integration of many mental ray features in Maya, including features currently not made available in the UI by Autodesk at all. I’ve been using the beta versions fairly regularly and have found it excellent! A much nicer passes system, new shaders, cleaner linear workflow and many other offerings make this an excellent workflow enhancer. Check out a bunch of YouTube clips covering the whole system.
Introductory pricing lasts until the 15th of January and I’ll be picking up a copy myself!