The Nation's Invasive Species Information System:
http://www.invasivespecies.gov./

USDA National Invasive Species Information Center:
http://www.invasivespeciesinfo.gov/

USDA Forest Service Invasive Species Program:
http://www.fs.fed.us/invasivespecies/index.shtml 

USDA National Agricultural Library:
http://www.invasivespeciesinfo.gov/unitedstates/mi.shtml

National Invasive Species Council (NISC)
http://www.invasivespeciesinfo.gov/council/main.shtml