http://www.ma-eppc.org/ This link is for the Mid Atlantic Exotic Plant Pest Center which focuses on our region
http://plants.usda.gov/ Natural Resource Conservation Service database which is searchable for native plants
Gardening for special needs:
www.gardenforever.com for those of us who creak and moan more than we used too. It also is a great site for those of us who have a have a disability and are not ready to give up our favorite hobby or passion.
http://www.nwf.org/gardenforwildlife/ This site is full of information which will help you plan, plant and then certify your property as a Certified Backyard Habitat
http://www.xerces.org in praise of pollinators... this site will show you the importance of bees, butterflies and all those" pests" to whom we rely on for our fruits and vegetables.