Hi Sean, as far as I know there's not a list of approved components, although there is a list of approved computers somewhere. Most of the computers on the list are a little old, but still working great for some users.
Here's a link to a recent build from Intel Doc. It's down the page a little.
http://duc.digidesign.com/showthread.php?t=274137
My computer build is in my profile. It's not proven with HD3, but works great with my HD2/i7.
About 3 or 4 pages back in this forum, there's some threads with pretty recent builds and there descriptions. I don't really keep up with the various components people are using until I'm ready to do a fresh build myself.