Shingles, Shakes & Tiles
GreenLivingIdeas.com

Metal Roofing
Cool Metal Roofing Coalition

Living Roof (Green Roof)
What is it? - Wikipedia.org
Toolbase.org

Membrane Roofing
EPDM: what is it? - EPDM Roofing Association
Wikipedia.org
TPO: what is it?

Information Resources
GreenRoofs.com
RCI-Mercury - online searchable library of roofing materials