current data and visualizations: CO2 ppm

Want to know how much CO2 is in the atmosphere daily?
http://co2now.org/

Animated graph of the increase in carbon dioxide in the atmosphere from 1979 to present:
http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html

June update: data indicates we have passed the 400 ppm mark
http://www.wri.org/blog/400-ppm-carbon-dioxide-levels-cross-sobering-new-threshold

Here's what the EPA has to say about the issue (the visualizations and models of different scenarios, ranging from low to high emissions)
http://www.epa.gov/climatechange/science/future.html

If you want the data, IPCC consolidates and synthesizes it into a report each year.
http://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml

oh, yes, and then there is the competing vision (arguing that warming will be minimal and will have benefits), provided by the NIPCC.
http://nipccreport.org/reports/ccr2b/ccr2biologicalimpacts.html