The following are a few resources dealing mostly with lumber:
Wood Handbook: Wood as an Engineering Materialhttp://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.pdf
Wood Web, a resource providing general knowledge regarding lumber. Their knowledge base provides information regarding adhesives, millwork, business, and cabinet making, laminating, wood engineering and many other topics.
Southern Pine By Design FAQ
Article about Warping and Drying in Lumber, and few others if you go a little further back in the directory.