My mom (who gets all of her news from AOL, we'll forgive her though) sent me this article about the top ten invasive species in the United States. The species were ranked based on the financial impact they have on the United States each year, but I think invasive species are interesting because of the environmental questions they raise.
What constitutes a truly natural environment?
Are all invasive species bad?
How do ecosystems interplay with each other?
How do humans affect wildlife through other organisms?
What kind of legacy has the presence of humans left the world?
Things to think about, if you like that sort of thing.