Links on Hand Building Steel Bicycle Frames
Little Fish Bicycles has quite a bit of information, including on building an 8020 brazing jig.
Paragon seems to have some useful stuff like tube blocks for jigging, etc.
A good list of links by Josh Putnam.
Link to a bikeforum.net step by step pictoral of a really nice build.
Nova seems to have a lot of parts and information.
Tim Paterek has published his book, The Paterek Manual for Bicycle Framebuilders on the web in PDF format. Please note that this is the version from 1983, and a more up to date version can be purchased from his site.