Identifying birds by sight and sound
Professional Organizations
Examples of other bird club web sites
Bird Quizzes
Web sites with many birding topics
Other birding information of various types

Identifying birds by sight and sound:

Dendroica (many songs and photos per species)
Cornell University Bird Guide
Cornell Macaulay Sound & Video Catalog
Whatbird.com: online Field Guide with pictures, songs, descriptions, and range maps
Identify songs by selecting attributes
Learn Bird Songs!
USFWS Atlas of Feathers
Patuxent Bird Id InfoCenter
Patuxent Wildlife Research Center songlist

iPodT/iPhone/iPad: Sibley eGuide to the Birds of North America
iPod/iPhone/iPad: Birdjam - bird songs from the Stokes DVDs
iPod/iPhone/iPad: iBird Explorer PRO - Guide to the Birds of North America
iPod/iPhone/iPad: Peterson Birds of North America
iPodT/iPhone/iPad: National Geographic field guide

Professional Organizations:
American Birding Association
American Ornitholgist's Union
Cornell Lab of Ornithology
National Audubon Society
Pennsylvania Society for Ornithology
Wilson Ornithological Society
Birdnet (Ornithological Information)
Selected bird/birding club web sites:
PSO's list of PA birding organizations
Baltimore Bird Club
Cincinnati Bird Club (OH)
Delaware Vally Ornithological Club
Howard County (MD)
Lancaster Bird Club
Lehigh Valley Audubon Society
New Jersey Audubon Society
Northern Virginia Bird Club
Presque Isle Audubon Society
Seneca Rocks Audubon Society

Southern Maryland Audubon Society
Todd Bird Club
Tiadaghton Audubon Society
Three Rivers Birding Club
North American Bird Clubs
Websites about the general topic of birding:

birding.com's list of it's top 25 Birding Websites
Cornell Lab of Ornithology YouTube Channel
All-birds.com
birding.about.com
Birdwatching.com
birdingonthe.net
Birdzilla.com
wildbirds.com

Other birding information of various types:

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
Virtualbirder.com: Take a virtual online tour of birding locations
Bird Watcher's Digest
Peterson Online
Hawk Mountain Sanctuary
Middle Creek WMA information
Middle Creek WMA waterfowl update
Cape May Bird Observatory
Cape May Birds and Birding
Cape May Hawk Watch
Pennsylvania Game Commission
Google maps (maps and trip directions)
Yahoo maps (maps and trip directions)
Bing maps (maps and trip directions)
Mapquest (maps and trip directions)