Whatbird.com
This is a great resource if you're having trouble identifying a bird. The forums are particularly helpful

Birding Forecasts
An up to date great place to check on when birds are moving by date and region

Project Feeder Watch
An interactive list of almost 100 common feeder birds and cross referenced what they like to eat and where they like to eat it. Explore your region to see what you might be able to attract to your feeder this winter!

Birding Hotspots
Want to know where the birds are hanging out close to where you're hanging out? This interactive map will show you birding hotspots throughout the US and world.

Merlin
This a great free app for iPhone and Android devices that will help you identify birds in the field. The interface is supper easy and includes photos and bird songs and sounds for reference.

I-Bird
This is probably my favorite bird identification tool. It's not as easy to use as Merlin, but it's much more robust and contains a larger bird database and more information. It's available for purchase for multiple devices. There are actually several apps in the suite and they are often bundled at a discounted price. Definitely worth the purchase price!