Better Homes and Gardens Plant Finder - http://www.bhg.com/bhg/plantfinder/
Ignore the ads and find thorough information about all types of plants including but not limited to: flower color, light preferences, height and fragrance.
Gardening Programs & Resources - http://www.metrokc.gov/dchs/csd/wsu-ce/Gardening/
Washington State University King County, Cooperative Extension Resources for Home Gardeners, including top WSU web site Gardening in Western Washington
GardenWeb - http://www.gardenweb.com
GardenWeb contains forums to chat with other gardeners, plant database with images and a glossary of botanical terms. The site also includes directories, events and regional information.
Helpful Gardener - http://www.helpfulgardener.com
The Helpful Gardener brings the pleasure of gardening to your home. This site is continually adding new articles, gardening tips and features for all aspects of gardening.
Trees Are Good - http://www.treesaregood.com
The International Society of Arboriculture offers brochures on tree care - subejcts include buying high-quality trees, tree care, pruning, topping, and insect/disease problems.