Intergovernmental Panel on Climate Change http://www.ipcc.ch/.
Climate Change 2007: The Physical Science Basis: Summary for Policymakers http://www.ipcc.ch/SPM2feb07.pdf [PDF].

This entry at RealClimate: Climate science from climate scientists seems to me a good introduction to refuting global warming deniers.

Websites, etc. about global warming and the global warming deniers:

RealClimate: Climate science from climate scientists

The Discovery of Global Warming by Spencer R. Weart.

CBC News: the fifth estate - The Denial Machine a documentary broadcast in November 2006, identifies the global warming deniers; the Resources webpage of The Denial Machine also lists global warming deniers' websites. The following links (refuting the deniers) were obtained from that page.

DeSmogBlog: Clearing the PR Pollution that Clouds Climate Science

The Heat Is Online

Think Progress

ExxonSecrets.org: How ExxonMobil Funds the Climate Change Skeptics

David Suzuki Foundation: Climate Change Skeptics

Monbiot.com [Motto: Tell people something they know already and they will thank you for it. Tell them something new and they will hate you for it.]

Climate Science Watch