Thanks to Jeanne LeBlanc of ctnow.com for compiling some of these links…
The University of Connecticut Plant Database shows photographs and describes plant habitats, habits and forms, summer and autumn foliage, flowers, fruit, bark, optimal growing/site conditions, landscaping use, drawbacks, identification features, propagation, and cultivars/varieties, as well as audio pronunciation recordings for botanical names! They also have a Plant Selector which helps you choose a plant based on lists of various characteristics that you can select.
The USDA Plants Database has a comprehensive encyclopedia of information on vascular plants, mosses, liverworts, hornworts, and lichens. It provides information similar to that in the UConn Plant Database, but covers the entire U.S. and its territories.
The Connecticut Botanical Society has information on Connecticut native plants for the garden, photos and information about 400 Connecticut wildflowers, and a gallery of fern photos.
The Connecticut Agricultural Experiment Station has information about upcoming events, a Plant Pest Handbook, and archives of bulletins and fact sheets on various topics.
The University of Connecticut Integrated Pest Management Program has information on various plant pests, diseases, and weeds.
GardenWeb has forums where you can ask questions, a plant database, lists of gardening tips, a directory of plant organizations, a section devoted to information on roses, and a glossary of botanical terms.
About.com also has a wealth of information, links, and articles relating to gardening.
ctnow.com archives its news articles about gardening.