Backyard Wildlife Habitat is the National Wildlife Federation's program to help gardeners plan their landscape with the needs of wildlife in mind, and to give them the tools they need to make it happen. It's Questions on Plants page provides information on the use of native plants.
Invasivespecies.com is the gateway to Federal efforts concerning invasive species.
Invasives on the Web is The Nature Conservancy's site on invasive plants.
Invasive and Exotic Species of North America provides an accessible and easily used archive of high quality images related to invasive, introducted or exotic species, with particular emphasis on educational applications. Of particular interest is their page on Invasive Plants of the Thirteen Southern States and Exotic Pest Plants of Southeastern Forests.
IPlants: Invasive Plants and the Nursery Industry is an interesting undergraduate thesis on invasive plants.
The Plants Database is a source of standardized information about plants.The Plant Conservation Alliance's Alien Plant Working Group site entitled "Weeds Gone Wild" provides information for the general public, land managers, researchers, and others on the serious threat and impacts of invasive alien (exotic, non-native) plants to the native flora, fauna, and natural ecosystems of the United States.
The Southeast Exotic Pest Plant Council is a non-profit organization established to raise public awareness about the spread of exotic plants into the southeast's natural areas. Its State Chapters include Florida, Georgia, Tennessee, North Carolina, Mississippi, Kentucky, and Alabama.
The Southern Appalachian Information Node (SAIN) is SAMAB's partner in providing a gateway to regional biological information. SAIN is a part of the National Biological Information Infrastructure (NBII), a broad, collaborative program to provide increased access to data and information on the nation's biological resources. See their page on Invasive Species.