The United Nations Environment Programme (UNEP) -- provides data, graphs and maps on a variety of environmental issues. A menu of data sources is available at http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=293 . The main country level data base is the GEO data portal which has time-series data on more than 400 indicators. This data base will provide data as downloadable files in a number of formats including .csv and .xml. The downloads include both the ISO 2 and 3 character country codes for easy linking to other data bases. The GEO Data Portal is available at http://geodata.grid.unep.ch/ .
United Nations -- Data on the environment indicators related to the Millennium Development Goals is available at http://unstats.un.org/unsd/mi/mi_goals.asp .
World Bank -- The World Bank provides environment data in time series on the World Development Indicators (WDI) at http://databank.worldbank.org/data/databases.aspx . You can get the data for the latest year for a single country from links on http://data.worldbank.org/topic/environment .
Gapminder -- Gapminder is an innovative data presentation web site that provides dynamic views of data changes over time using bubble graphs. Graphs are available for economic, population, health, environmental, agricultural and information technology data. Raw data can be downloaded from the site and a desktop version of the software is available free. Users can customize graphs using existing data, but cannot add new data. Much of the data used is from the World Bank and UN organizations. Gapminder is at http://www.gapminder.org .