International Union for Conservation of Nature and Natural Resources Red List of
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 GEO 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 450 different variables at national, subregional, regional and global data or as geospatial datasets (maps)". The data here cover a wide range of themes and topics, including biodiversity and threatened species.
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. Data for the EPI are available either for download or via tools to rank and compare countries' index scores.
Environmental Sustainability Indicators and Trends
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.
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.
World Resources Institute - Maps & Data
The World Resources Institute has compiled a variety of data resources on topics such as emissions and agriculture.