Want to go into DfE in more depth? Here are some some print based materials to read. The web is great for staying up to date, but there is nothing like high-quality, well-edited, peer-reviewed print material to introduce a topic.
Otto K, Wood K (2001). Design for the Environment. Chap. 15 in Product Design: Techniques in Reverse Engineering and New Product Development, Prentice Hall. Excellent introduction to DfE for the product designer.
Datschefski E (2001). The Total Beauty of Sustainable Products", RotoVision. Wonderful case studies of designed products where DfE was taken seriously. A coffee-table style book where the book itself is beautiful to look at.
Graedel T, Allenby B (1996). Design for Environment, Prentice-Hall. Introduces the life cycle approach. Widely cited book on DfE.
Billatos S, Basaly N (1997). Green Technology and Design for Environment, Taylor & Francis. Good introductory text, complete with case studies.
Green@work Good way to stay up to date on green design issues and policy.
Bettery by Design, Minnesota Pollution Control Agency
Designing for the Environment. An excellent guide from the American Plastics Council. Covers design issues related to designing enclosures. Nice sections on fastening and joining.