British Petroleum Statistical Review of World Energy--The Statistical Review of World Energy is a very good source for international time-series data on energy production and consumption, with a collection of downloadable data here.
Carbon Dioxide Information Analysis Center (CIDAC)--The CDIAC is an excellent source for comprehensive data on climate change and related matters. Users may be especially interested in Trends Online, which includes much historical data on CO2 emissions as well as historical data on average temperatures.
Climate Data Online--The National Oceanic and Atmospheric Administration's Climate Data Online site is an access to climate data maintained by the National Centers for Environmental Information. You can access data collected via means such as land-based monitoring stations, satellites, or sea-based observation stations, measuring topics such as temperature and amount of sunlight and amount of precipitation. The Quick Links will take you to many of the available data collections.
Department of Energy Energy Information Administration (EIA)--The EIA is a very extensive source for data on energy consumption in the United States, with both annual and monthly data available. The EIA also has a collection of "navigators" with additional data on various categories of energy, such as the Petroleum Navigator that includes national and state-level data on prices, production, and consumption. The EIA also has much international data available.
Emergency Events Database (EM-DAT)--EM-DAT provides data on sizes of affected populations from different categories of diasters, both natural (e.g. floods, landslides, earthquakes, drought) and technological/human-made (e.g. industrial accidents, transporation accidents). You can query the data or request access to the complete database.
Environmental Performance Index (EPI)--Yale University's Environmental Performance Index scores countries in two main areas of environmental performance: protection of human health and protection of ecosystems. Countries are further scored on sub-categories such as air quality, biodiversity, forests, and water resources. There are various tools to rank and compare countries' index scores, and the EPI data are also available for download. Data from this project are also available via Columbia University's Socioeconomic Data and Applications Center. The EPI data are also included within the Quality of Government Institute's Standard Data.
Environmental Sustainability Index (ESI)--The ESI is a project of Yale University and Columbia University that scores and ranks countries on their abilities to provide long-term environment protection. Data from ESI reports are available in both .pdf and Excel formats.
Environmental Sustainability--This site, which is hosted by Columbia's Socioeconomic Applications and Data Center, compiles links to various sources for data and other sources on sustainability. Be sure to check out SEDAC's other data resources for data on other environment-related topics such as climate, environmental governance, land use, and water resources.
Environmental Treaties and Resources Indicators (ENTRI)--ENTRI is a searchable database of environmental treaties that allows users to create profiles of particular countries with regard to environmental treaties and agreements. Users can also search for treaties by topic of coverage and search through or browse full texts of treaties.
Paul Hensel's International Environmental Data Page--This site, which is hosted by Dr. Paul Hensel, contains links to data on a variety of environmental topics such as fisheries, energy, water disputes, and agricultural production.
International Environmental Agreements (IEA) Database Project--The University of Oregon's IEA Database Project is compiling information on multilateral and bilateral environmental agreements to identify membership in those agreements and code the contents of those agreements in terms of areas covered and legal provisions within them. The data collected and coded by this project are intended for use in measuring the effects of such agreements on environmental outcomes.
International Union for Conservation of Nature and Natural Resources Red List of Endangered Species--The IUCN's Red List of Endangered Species allows users to create lists and summaries of endangered or threatened species by taxonomy, extent of threat, and/or geography (e.g. countries, maritime regions).
United Nations Environmental Programme Data Portal--To quote the website, "[the] GEO Data Portal is the authoritative source for data sets used by UNEP and its partners in the Global Environment Outlook GEO) report and other integrated environment assessments. Its online database holds more than 400 different variables, as national, subregional, regional and global statistics or as geospatial data sets (maps), covering themes like Freshwater, Population, Forests, Emissions, Climate, Disasters, Health and GDP." Researchers are able to download the data in multiple formats.
United Nations Food and Agriculture Organization (FAO) Statistics--The FAO is a UN organization that is ostensibly devoted to alleviating world hunger. The FAO's collection of statistics and databases covers a variety of topics, such as water, agricultural production, and agricultural consumption. The geographic and time coverage vary by topic and database. Users can query the databases to create extracts of data of interest or can download the data in bulk.
World Bank Environment--This World Bank site contains links to various resources, including collections of environmental data and statistics. The Bank also produces more specialized data collections, such as the Wealth of Nations data on the sustainability of countries' growth trajectories and the Adjusted Net Savings data that incorporate the effects of environmental depletion. See also the environmental data section within the Bank's data collections.
World Resources Institute - Maps & Data--The World Resources Institute has compiled a variety of data resources on topics such as emissions, locations of power stations, usage of clean technologies, and agriculture.