With the success of Project Vasari, more designers are becoming interested in learning to harness the power of conceptual design tools. The following is a short list of the best resources I have found.
Autodesk University – AU Archives A great resource for all Autodesk products. Often contains recorded presentations on a variety of topics in Revit.
Autodesk Wiki – A new resource in the 2012 release that includes videos, documentation and contributions from users.