Links for tree and wood species identification:

Birch Trees – http://uptreeid.com/Species/Birch.htm
Maple Tress – http://uptreeid.com/Species/maples.htm and http://www.massmaple.org/treeID.html

Multiple Trees, including print-out color PDFs
http://www.uwsp.edu/cnr/leaf/treeid.shtml

From Duke U:
http://www.duke.edu/~cwcook/trees/#trees

Common woods in Appalacia (oak(s), Ash, Cherry, Hickory, Beech, Black Walnut)
http://www.appalachianwood.org/species/species.htm

Wood of the Mid Atlantic (oaks, poplars, etc.)
http://www.growingnative.org/pcgn_treeid.html

Arbor Day Foundation Site:
List of Eastern Tress with ID drawings: http://www.arborday.org/trees/ECtreelist.cfm
List of Western Trees with ID drawings:http://www.arborday.org/trees/wtreelist.cfm
What Tree is that? (guide): http://www.arborday.org/trees/treeID.cfm

Forestry Types of the US – along with IDs
http://forestry.about.com/library/tree/bltypdex.htm[/url]

About.com Guides:
Hardwoods – http://forestry.about.com/cs/treeid/a/hard_tree_id.htm
Conifers – Soft Woods – http://forestry.about.com/cs/treeid/a/con_tree_id.htm