Biological Control: A Guide to Natural Enemies in North America, Cornell University, Department of Entimology: Information and pictures on beneficial insects.
Cornell Garden-Based Learning, Cornell University, Department of Horticulture: General gardening information and tips on growing specific vegetables
International Seed Saving Institute: Fact sheets about seed saving and vegetables whose seeds are easy to save
National Center for Home Food Preservation, University of Georgia: a complete source of information about food preservation
National Climate Data Center, National Oceanic and Atmospheric Administration: "The world's largest archive of climate data" including average frost dates and worldwide climate data.
National Institute of Food and Agriculture, USDA: lots of great information and local coop extension office locators.
Ohioline: Yard & Garden, Ohio State University, College of Food, Agriculture, and Environmental Sciences: General gardening information and tips on growing specific vegetables.
Saving Vegetable Seeds: Tomatoes, Peppers, Peas and Beans, University of Minnesota Extension, article on vegetables whose seeds are easy to save.
Sustainable Agriculture Research and Education: Information and publications on sustainable agriculture, including cover crops.
Vegetable IPM, Texas A&M University: Excellent garden pest photos and "dedicated to integrated pest management for the home vegetable gardener"
What's Wrong with My Plant?, University of Minnesota Extension: help you identify vegetable plant diseases