Oceanic and atmospheric climate data. Climate Prediction Center, National Weather Service, NOAA. In particular, monthly atmospheric and sea surface temperature indices (for the tropics).
Gridded climate datasets. Earth System Research Laboratory, NOAA. In particular, the NCEP/NCAR Reanalysis data.
Sea surface temperatures. National Climate Data Center, NOAA.
Climate data. Climate Research Unit, University of East Anglia.
Intergovernmental Panel on Climate Change (IPCC) Data Distribution
Centre.