- NCAR's Climate Data Guide (new and very nice)
- Columbia's IRI/LDEO Climate Data Library (interfaces with OPeNDAP, making download easy)
- NOAA's Earth System Research Laboratory Gridded Data Collection
- Reanalysis.org (discussed briefly here)
- IPCC Data Distribution Center (both historical and future projections are here)
- RealClimate Data Sources Page
All of these sites are listed in our meta-resources page.