A handful of useful sites dealing with wood:

FPL:
- intro-page of the Forest Products Laboratory:
http://www2.fpl.fs.fed.us/

- technical properties of wood
http://www2.fpl.fs.fed.us/TechSheets/techmenu.html
including two downloadable books on US-woods

- the FPL "Wood Handbook. Wood as an engineering material"
(downloadable):
http://www.fpl.fs.fed.us/documnts/FP.../fplgtr113.htm

- common and scientific names of wood
(best database around, with a fairly low level of error):
http://www2.fpl.fs.fed.us/CommNames2000.html
[apparently off-line more often than not, and usually reports:
"The system has encountered an error that was logged"]

OTHER SOURCES:
- "The American Woods" (pictures):
http://www.lib.ncsu.edu/archives/forestry/hough/

- lots of pictures (fun), but short on accuracy and real information
full version (slow):
http://www.hobbithouseinc.com/person...indextotal.htm
small version (faster):
http://www.hobbithouseinc.com/person...pics/index.htm

- for a more extensive link-page see:
http://www.nehosoc.nl/paginalinks.htm

BOOKS:
entry-level books on wood are
"Good Wood Handbook" by Albert Jackson & David Day (cheapest and best)
"Woodworker's Guide to Wood" by Rick Peters (passing grades)
"Woodworker's guide to Selecting and Milling Wood" by Charles Self
(somewhat modest, pictorially, but written in a friendly style)
"Harvesting Urban Timber" by Sam Sherrill

Adult books on wood are
"Understanding Wood" by R. Bruce Hoadley
"Identifying Wood" by R. Bruce Hoadley

For those not shying away from a thick book:
"Holzatlas" by Rudi Wagenfuhr