http://theoildrum.com Perhaps the premiere site for the determination of the peaking process as it unfolds.

http://globalpublicmedia.com/INTERVIEWS interviews concerning peak oil related issues

Earth Spirit Earth Crash: Healing Ourselves and a Dying Planet (Source Material on Ecosystem Destruction & Collapse, Loss of Biodiversity, Endangered Species & Extinction, Global Warming & Climate Change, Pollution, Over-population)
http://eces.org/index.shtml

Association for the Study of Peak Oil
http://www.energiekrise.de/e/index.html

Oil Analytics
http://www.oilanalytics.org

Technocracy: a "scientific rational" approach to society's dependence on energy
http://www.technocracy.ca/simp/start.htm

Mission: assemble, study, and disseminate global oil supply data
http://hubbert.mines.edu

A collection of expertise on the Peaking of Oil, in memory of M. King Hubbert.
http://www.hubbertpeak.com

Famous and extensive site on the Peaking of Oil: from the perspective of Scientific Materialism, leading to utter despair.
http://dieoff.org