The online version of "E - The Environmental Magazine" has a story in the May/June issue about invasive species. It's a well-written piece that focuses on animals, and has what is possibly the cutest photo I've ever seen of a feral hog (the endangered species look good too :-). If you're not familiar with the issues surrounding invasive animals, this article is a good introduction. There are a few references in the article to an excellent "layman's" book on the subject of invasive species, Kim Todd's Tinkering with Eden, if you prefer book-learning to web-learning.
(Thanks to a member of the ALIENS-L listserver for posting the link to this story.)