The Fundamental Physical & Chemical Constants database gives values of the basic constants and conversion factors of physics & chemistry as published by CODATA (Committee on Data for Science & Technology) and the NIST in 2002. Updates for 2006 are also available.
The site also includes conversion factors for energy equivalents recommended by CODATA for international use. For more information and to start searching look @ http://physics.nist.gov/cuu/Constants
