The Oil Drum

Please do read this first one thoroughly, it is a well substantiated and quite scary review of research that points to very rapid climate change:
http://www.aip.org/history/climate/rapid.htm

The rest of this post has grown a bit like Topsy, some good links though, hope someone finds them of use. I'm sure I have more good links, especially about methane release from tundra and ocean bed hydrates, but can't find them atm.

IPCC TAR reports 2001 available as html here:
http://www.grida.no/climate/ipcc_tar/
IPCC main site:
http://www.ipcc.ch/

On rapid / abrupt climate change:
http://earthobservatory.nasa.gov/Study/Paleoclimatology_Evidence/paleoclimatology_evidence_2.html
http://www.wunderground.com/education/abruptclimate.asp

Sea level:
http://www.atse.org.au/index.php?sectionid=323
http://www.linkvoyager.com/cgi-bin/serve.fcgi/climate_change_science/global_sea_level_rise/
http://www.geus.dk/geuspage-uk.htm

Antarctica melting would be the final and most dramatic cause of sea level rises, it ain't going to happen to a significant extent for probably hundreds of years. But some parts like the West Antarctic Ice Sheet are more at risk than others:
http://www.antarctica.ac.uk/Key_Topics/IceSheet_SeaLevel/index.html

And if you want to see maps of what floods:
http://flood.firetree.net/

Green house gases
http://www.ghgonline.org/index.htm  (lots of good stuff if you dig)
http://www.ncdc.noaa.gov/oa/climate/gases.html

Atmospheric CO2 lifetime (IPCC gives as 5 to 200 years)
http://www.grida.no/climate/ipcc_tar/wg1/016.htm
http://cdiac.esd.ornl.gov/pns/current_ghg.html
This is as good an overview as I've found:
http://www.ess.uci.edu/~reeburgh/fig1.html
http://www.ess.uci.edu/~reeburgh/pics/010.jpg
...and its parent page has other cycles:
http://www.ess.uci.edu/~reeburgh/figures.html

CO2 trends
http://www.cmdl.noaa.gov/ccgg/trends/

Biogeochemical cycles
http://www.dpc.ucar.edu/globalChange/index.html

Methane: permafrost and tundra
http://gsc.nrcan.gc.ca/permafrost/climate_e.php
http://www.ulapland.fi/home/arktinen/tundra/tundra.htm

Methane: ocean floor hydrates / clathrates
http://www.ghgonline.org/methanehydrates.htm
http://gsc.nrcan.gc.ca/permafrost/arcticgas_e.php

Other good links
http://eos-webster.sr.unh.edu/climate_change.jsp  (good portal)
http://stephenschneider.stanford.edu/Climate/Climate_Science/CliSciFrameset.html  (good source)
http://www.aip.org/history/climate/index.html
http://www.ucar.edu/research/climate/
http://www.usra.edu/esse/essmp/essmp.html
http://www.cru.uea.ac.uk/cru/info/
http://lgmacweb.env.uea.ac.uk/esmg/welcome.html
http://lwf.ncdc.noaa.gov/oa/ncdc.html
http://www.met-office.gov.uk/research/hadleycentre/links.html
http://www.climatehotmap.org/impacts/index.html
http://www.newscientist.com/channel/earth/climate-change/
http://www.whoi.edu/institutes/occi/topicIndex.do?o=read&id=464
http://www.realclimate.org/
http://www.climatescience.gov/

I would add a personal opinion: if significant ocean bed methane is now being released there will be major climate change and global warming within 50 years and human population will drop by at least 50% from current levels by 2100 and be confined to the coldest global regions even if there are no massively destructive human wars - Lovelock's latest prognostications would come true. I don't believe a video of possible methane bubbles from ocean sediments constitutes sufficient evidence for significantly increased gasification of ocean floor methane hydrates (methane has probably been bubbling from the ocean floor for millions of years), I will wait for some decent scientific papers. However, we have no way of knowing with any certainty what would trigger large scale ocean floor methane hydrate release. Nor have we sufficiently validated models for the effects of permafrost melting on methane and carbon dioxide release to enable us to predict its effect on atmospheric greenhouse gases. Both these effects are (probably totally) positive feedback loops in the greenhouse gas increase sense: once started they will run their course.

We could already be past the point of no return or we could have decades of business as usual greenhouse gas emission to go before Earth's climate is committed to a catastrophic (for human and most 'higher' lifeforms on this planet) path. But there is a probably logical conclusion one could draw based on our geological analysis of climate: if we released nearly all earthly fossil hydrocarbons into the atmosphere we should expect global climate to become as warm as it has ever been in the last 500 million years.