Corals
ReefBase

Diatoms
Canadian Diatom Database
Diatom Paleolimnology Data Cooperative
European Diatom Database

Foraminifera
PLANKRANGE database
South Florida Ecosystem History Project

Lakes
LakeNet
National Lacustrine Core Repository
Global lakes and wetlands database

Oceans
Antarctic and Southern Ocean Data Portal
International Arctic Science Committee (IASC)
British Oceanographic Data Centre
CCHDO/CLIVAR - CLIVAR & Carbon Hydrographic Data Assembly Office
CLIVAR Data
Deep Sea Drilling Project
Delphi Project
Global Ocean Data Analysis Project
Global Ocean Observing System
Global Plankton Database
Integrated Ocean Drilling Program
Japan Oceanographic Data Centre
Joint Global Ocean Flux Study
Marine Seismic Data Center
NOAA/NDGC - Marine Geology and Geophysics
North Pacific Marine Science Organization (PICES)
USGS - Coastal & Marine Geology InfoBank
University of Washington Quaternary Isotope Laboratory data sets

Ostracodes
Arctic Ostracode Database
North American Non-Marine Ostracode Database (NANODe)

Astronomy and Atmosphere
British Atmospheric Data Centre
Canadian Astronomy Data Centre
Carbon Dioxide Information Analysis Center
Centre de Données astronomiques de Strasbourg
NASA National Space Science Data Center
Solar Influences Data Center
Space Science and Engineering Data Center
World Data Centre for Greenhouse Gases

Climate
Canadian Centre for Climate Modelling and Analysis
Climate Impacts LINK Project
IRI/LDEO Climate Data Library
IPCC Data Distribution Centre
KNMI Climate Explorer
Links to atmospheric and oceanographic data sources
Met Office Hadley Centre

Modeling
IPCC Data Distribution Centre
World Data Center for Climate

Environmental isotopes

Arctic LTER database
Environmental Isotope Database
Global Network of Isotopes in Precipitation (GNIP)
Global Network of Isotopes in Rivers (GNIR)
Global Seawater Oxygen-18 Database
Isotope Hydrology Information System (ISOHIS)
Isotopes in Groundwater, Lakes, Springs and Streams
Moisture Isotopes in the Biosphere and Atmosphere (MIBA)
National Atmospheric Deposition Program
National Institute of Standards and Technology Database
Phanerozoic and Precambrian Isotope Databases
Stable Water Isotope Intercomparison Group (SWING)
Water Isotope System for Data Analysis, Visualization, and Electronic Retrieval (WISER)

Documentary Data/Archeology
China Data Center 
Euro-Climhist - Ways to weather hindcasting
National Archeological Database
Norwegian Historical Data Centre
Social Sciences Data Collection
World Data Center for Human Interactions in the Environment

Early Instrumental
The Comprehensive Historical Upper-Air Network (CHUAN)

Borehole Data
Borehole Temperatures and Climate Reconstruction Database
Links to USGS borehole data

Dendrochronology
Euro-dendro
Dendrochronology GIS
International Tree-Ring Data Bank

Fire
International Multiproxy Paleofire Database
USFA National Fire Data Center

Geology/Geomorphology/Paleoenvironment
Alaska PaleoGlacier Atlas
Antarctic Digital Gravity Synthesis (ADGRAV)
Earth Resources Observation and Science (EROS)
GEOSCOPE
National Geoscience Database of Iran
Neotoma - Paleoecology Database

Paleobiology/Paleontology
Biostratigraphy
FAUNMAP
New Mexico Paleo-Database
Paleobiology Database

Paleobotany
Australasian Pollen and Spore Atlas (APSA)
BIOME 6000
Canadian Pollen Database
New England Lakes Plant Macrofossil Database
NOAA Plant Macrofossil Database
North American Modern Pollen Database
Northern Eurasian Palaeoecological Database
PMIP 2

River Runoff
Global Runoff Data Centre

Snow and Ice
Advanced Cooperative Arctic Data and Information Service (CADIS)
Alfred Wegener Institute for Polar and Marine Research
Australian Antarctic Data Centre
International Polar Year (IPY) GCMD Portal
National Snow and Ice Data Center
World Data Centre for Glaciology
World Glacier Monitoring Service

Soils
European Soil Portal
Soil Erosion Data

Tephra
Alaskan tephra data
Large Volume Explosive Eruption Database
Mono-Inyo Craters Database
Tephrabase
Volcanoes Database