Learn more about the history of the Earth’s climate and climate modeling at these online resources to go along with Episode 6 of Walkabout the Galaxy, our special Memorial Day discussion of global climate change.
There are a lot of excellent graphical representations of climate data at this site, aggregated from various source sites. http://www.skepticalscience.com/graphics.php
NASA’s climate science portal page is here.
This site addresses some of the common claims against evidence for global climate change or global warming. (You can also easily find on line roughly a gazillion sites providing arguments denying present or imminent climate change.)
The Intergovernmental Panel on Climate Change (IPCC) publishes exhaustive reports on climate change including analysis of climate data and model projections under a variety of different assumptions about future greenhouse gas emission. Their most recent report (AR5) is available at their site.