A few links to start you off:

Real Climate: a blog of scientists' comments on climate change

EPA website on climate change

The Intergovernmental Panel on Climate Change

Grist Magazine: Environmental news and articles with a sense of humor

Pew Center on Global Climate Change

"How to Talk to a Climate Skeptic" (addresses many specific questions in depths and includes additional links)

"The Truth About Denial"

Climate Choices: Information on warming in California and California's efforts to combat global warming