Every so often people ask me for references on Intel virtualization technology. Below are a few helpful links that have served me well, whether it's getting broadly clued in on a technology like VT-d or looking up the particulars of MSR bit semantics.

A good starting point for all things virtual at Intel is:

http://www.intel.com/technology/platform-technology/virtualization/

There are links from this site to the many other Intel information sources--IDF, research sites, blog sites, Intel Technology Journal, etc.