Here's a super informational pamphlet from the U.S. Fish & Wildlife Service.  It summarizes all aspects of backyard bird feeding such as types of food and feeders.  It also discusses the best home designs and landscaping for birds.

The Cornell Lab of Ornithology is a nonprofit membership institution whose mission is to interpret and conserve the earth's biological diversity through research, education, and citizen science focused on birds. Their programs work closely together and with citizen scientists, government and non-government agencies, and organizations across North America and beyond to learn more about birds, including how to best protect them and their habitats.

The American Birding Association aims to inspire all people to enjoy and protect wild birds.  Check out their Birders' Resources section for tips on identifying a new bird, where to go birding, and a brief guide to field guides and binoculars.

National Audubon Society -- This is an environmental conservation organization focused on birds, which maintains a web site with information about NAS activities and priorities, as well as a list of chapters by state, with links to chapter sites where available.

National Wildlife Federation -- Where you'll find education, inspiration and assistance to conserve wildlife and other natural resources.

Ways YOU can personally participate:

Cornell Lab of Ornithology -- Citizen Science Projects -- All across North America, thousands of people of all ages and backgrounds are participating in the Cornell Lab of Ornithology's research projects. From backyards and city streets to remote forests, these people represent the world's largest research team. We call them citizen scientists.  

Project FeederWatch -- a winter-long survey of birds that visit feeders at backyards, nature centers, community areas, and other locales in North America. FeederWatchers periodically count the highest numbers of each species they see at their feeders from November through early April. FeederWatch helps scientists track broad scale movements of winter bird populations and long-term trends in bird distribution and abundance.

The Great Backyard Bird Count -- Presidents' Day weekend in February of each year -- it will document the distributions and numbers of birds at the end of winter, the season of survival, before the spring migrations begin in March.  The data that you collect will be combined with Christmas Bird Count and Project FeederWatch data to give an immense picture of our winter birds. 

House Finch Disease Survey -- Do you have House Finches or American Goldfinches at your feeders?  Here is an unprecedented opportunity for you to help researchers track the spread of an infectious disease in a wildlife population.

Urban Bird Studies -- What birds live in your city? Whether you are a novice bird watcher or an expert, you can help answer this question by counting birds as you walk through your neighborhood.