Smithsonian Institution
National Museum of Natural History: Ocean Planet: Biological Roulette: Alien Species
Click on the roulette wheel and see how some alien species were introduced into the United States and the effect they have had on our country. This is part of an archived Smithsonian exhibit.
Other
Protect Your Waters: Non Native Species Impacts
This site offers a complete explanation of how invasive animals and plants impact many of the different things valued by Americans. The economic impact is enormous and estimated to be about $100 billion dollars per year.