Here are rather exhaustive lists of the skeptics' arguments on science grounds, along with brief analyses and links to underlying publications:
Further resources are here, for those interested:
Introductory:
NCAR: Weather and climate basics
Pew Center: Global Warming basics
Wikipedia: Global Warming
NASA: Global Warming update
NOAA, National Climatic Data Center Global Warming, Frequently Asked Questions: http://www.ncdc.noaa.gov/oa/climate/globalwarming.htmlThe Royal Society, climate change controversies: a simple guide, http://royalsociety.org/page.asp?id=6229http://www.brighton73.freeserve.co.uk/gw/globalwarmingfaq.htm
The Royal Society, Facts and fictions about climate change, http://royalsociety.org/page.asp?id=4761Climatic Research Unit, University of East Anglia, Information sheets, http://www.cru.uea.ac.uk/cru/info/
Tom Rees, “Global Warming: Answers to Frequently Asked Questions”,
History: Spencer Weart's excellent "Discovery of Global Warming" (American Institute of Physics)
Oxford University: The basics of climate prediction
The IPCC's AR4 Frequently Asked Questions (pdf).
Those with some knowledge:
RealClimate: Start with their "Start here" page, http://www.realclimate.org/index.php/archives/2007/05/start-here/
RealClimate's index: http://www.realclimate.org/index.php/archives/2004/12/index/
The IPCC reports themselves (AR4 2007, TAR 2001).
NOAA/NCDC: http://www.ncdc.noaa.gov/oa/ncdc.html; and "A Paleo Perspective on Global Warming", http://www.ncdc.noaa.gov/paleo/globalwarming/home.html
EPA, http://www.epa.gov/climatechange/index.html
The 2001 US National Assessment, http://www.usgcrp.gov/usgcrp/Library/nationalassessment/overview.htm;
http://www.usgcrp.gov/usgcrp/Library/nationalassessment/01Climate.pdf
National Center for Atmospheric Research, http://www.ncar.ucar.edu/
R. T. Pierrehumbert, Principles of Planetary Climate, http://geosci.uchicago.edu/~rtp1/ClimateBook/ClimateVol1.pdf (treatise)
Stephen Schneider, An Overview of the Climate Change Problem, http://stephenschneider.stanford.edu/Climate/ClimateFrameset.html
Roger Pielke Sr., http://cires.colorado.edu/science/groups/pielke/ and http://climatesci.org/
“THE PHOTOGRAPHIC DOCUMENTATION OF CLIMATE CHANGE”, http://www.worldviewofglobalwarming.org/
http://www.climateaudit.org/