The Astrophysics Data System (ADS)
The Astrophysics Data System (ADS) is a NASA-funded project which maintains four bibliographic databases containing more than 4.3 million records: Astronomy and Astrophysics, Instrumentation, Physics and Geophysics, and preprints in Astronomy. The main body of data in the ADS consists of bibliographic records.

Eric Weisstein's World of Physics
With 2700 entries, 14,065 cross references, 172 figures, and 22 animated graphics, this site is a wonderful portal into the world of physics. Listings are arranged alphabetically or by subject. Visitors to the site may also submit comments, suggestions, and corrections.

Glossary of Frequently Misused or Misunderstood Physics Terms and Concepts
Maintained by Donald E. Simanek of Lock Haven University, this site contains specific scientific meanings to words not accurately defined by general dictionaries. Created to help students with more difficult concepts, the site includes links to many othe resources. Additions, corrections, and suggestions for clearer statements and welcome by the site's author.

High Energy Physics Literature Database
HEP Indexes more fthan 5 million high enery physics articles, includes journal articles, technical reports, theses and conference papers.

NIST (National Institute of Standards and Technology)
NIST provides access to more than 80 scientific databases. Some of these databases are free. The databases cover many scientific disciplines, including physics and chemistry.

Physics Documents Worldwide
PhysDoc - Physics Documents Worldwide - offers lists of links to document sources, such as preprints, research reports, annual reports, and list of publications of worldwide distributed physics institutions and individual physicists, ordered by continent, country and town.

Physics related free access Journals
This site lists Physics related journals, which are freely available on the Web.