Dendrochronology

Ultimate Tree-Ring Pages
University of Arkansas Tree-Ring Laboratory
Lamont-Doherty Earth Observatory Tree-Ring Lab
University of Arizona Laboratory of Tree-Ring Research
The North American Dendroecological Fieldweek (NADEF)

Climate

Scripps Institution of Oceanography Climate Research Division
Global Change Master Directory
International Boundary and Water Commision
National Climatic Data Center (NCDC)
National Weather Service (NWS)
United States National Assessment on Climate Change
Desert Research Institute
National Geophysical Data Center
National Climatic Data Center
Time Biased Corrected Divisional Temperature-Precipitation-Drought Index
IRI/LDEO Climate Data Library
Climatic Research Unit