Pennsylvania Society for Ornithology
National Audubon Society
Cornell Lab of Ornithology
American Birding Association
American Ornitholgist's Union
Birdnet (Ornithological Information)

PSO's list of PA birding organizations
Tiadaghton Audubon Society
Three Rivers Birding Club
Delaware Vally Ornithological Club
Seneca Rocks Audubon Society
Lehigh Valley Audubon Society
Presque Isle Audubon Society
New Jersey Audubon Society
Howard County (MD)
Northern Virginia Bird Club
Cincinnati Bird Club (OH)
Baltimore Bird Club
Southern Maryland Audubon Society
United States Birding Clubs (Click on CLUBS)

Sibley Online Guide to Birds
Cornell University Bird Guide
Cornell Macaulay Sound & Video Catalog
whatbird.com's complete online Field Guide with pictures, songs, range maps, etc
Learn Bird Songs!
Feather Quest: identify birds by their feathers
National Geographic field guide in a handheld PDA
Patuxent Bird Id InfoCenter
Patuxent Wildlife Research Center songlist

birding.com's list of it's top 25 Birding Websites
birding.about.com
Birdwatching.com
birdingonthe.net
Birder.com
birdingguide.com

birdingpal.org: Birding contacts around the world
Birding in the Alleghenies
PA, Centre County, and Townships maps
Accessories: bigpockets.com
Birdsource: national and state Birding Projects
Fatbirder: linking birders worldwide
Central PA Birdline
Checklists for all states and selected parts of the world
Virtualbirder.com: Take a virtual online tour of birding locations
Bird Watcher's Digest
Peterson Online
Hawk Mountain Sanctuary
Cape May Bird Observatory
Cape May Birds and Birding
Cape May Hawk Watch
Pennsylvania Game Commission
Mapquest (maps and trip directions)
Google maps (maps and trip directions)