Center for International Earth Science Information Network
"CIESIN works at the intersection of the social, natural,and information sciences, and specializes in on-line data and information management, spatial data integration and training, and interdisciplinary research related to human interactions in the environment."
Data.gov
US government's open data collection
OECD Data
Browsable and searchable collection of latest OECD data, including charts, maps, tables and related publications. Browsable topics include Environment, Energy, Agriculture, and more.
United Nations Statistics Division: Environmental Statistics
Environment Statistics section of the United Nations Statistics Division.
U.S. Geological Survey Science Data Catalog
Includes extensive data on energy sources, water sources, and geographical characteristices and behavior.
World Development Indicators
World Bank data, includes extensive time series development indicators by country or area. Organize results in table, chart, map, or export data in a variety of formats.
World Resources Institute
Access WRI-produced maps, charts, data sets, infographics, and other visual resources.