The web sites of several organizations include statistics and rankings on many measures:

World Economic Forum
Organisation for Economic Co-operation and Development
World Health Organization
CIA World Factbook
United Nations
Photius.com
Aneki.com - Thousands of lists
WorldMapper.org - Over 700 maps scaled based on the measurement.
NationMaster.com - Compare countries
Wikipedia

Other sources or ranking information not used by the site, but of interest:

Gallup.com - Polls from the U.S.
Census.gov - Polls from the U.S.
Pew Global - Opinion polls from around the world.
AmericasHealthRankings.org - State by State data for many health measures.
InfoPlease.com - Ranks and lists of U.S. states trivia.
Top50States.com - Ranks and lists of U.S. states trivia.