The NIST Reference on Constants, Units and Uncertainty
Values recommended for international use by the Committee on Data for Science and Technology, International Council of Science. Navigation is by text search.

The Laws List
An alphabetical glossary of the various laws and theorems in this science.

Physics Formulae
A collection of frequently used physics equations compiled into several downloadable formats.

Physics FAQ (Where to Find It)
Links where to find the FAQ documents for physics.

Eqndb
Search for physics equations and constants by keywords and symbols.

The Physics Reference
Site contains every forumula a first-year physics student is likely to run into.