These are linked from the earthsummit 2012 web site:
Recent works defining "sustainabiity" and "sustainability science":
Evolution and structure of sustainability science by Luis M.A. Bettencourt and J Kaur PNAS 2011 vol. 108 pp 19540-19545
Sustainability Science: A room of its own by William C. Clark PNAS 2007 vol. 104 p. 1737
The Global Citizen articles by Donella Meadows, co-author of Limits to Growth.
350.ORG Begun by Bill McKibben of Middlebury College, 350.org takes its name from the safe upper limit of ppm of carbon dioxide in the atmosphere, and is now a global environmental activism movement focused on climate change.
GREENR: global reference on the environment, energy, and natural resources; see section on Sustainability