Physics 

Constants and Equations Pages - Divided into science, math and astronomy sections. The science pages include lists of constants and equations as well as conversion calculators.

Conversion of Units - An online conversion calculator from the Institute of Chemistry at the Freie Universität Berlin.

National Nuclear Data Center - The NNDC is a worldwide resource for nuclear data based at Brookhaven National Laboratory.  It specializes in nuclear structure and low-energy nuclear reactions, nuclear databases and information technology, and nuclear data compilation and evaluation.

Physical Reference Data - A series of online databases hosted by NIST containing physical constants, spectroscopy data, X-ray and gamma-ray data, radiation dosimetry data, and other physics data.

Review of Particle Physics Database - Annual description of properties of established and hypothetical particles, as well as related reviews and tools.  Published in Physics Letters B, v.667 (2008).

Table of Isotopes - Compiled and maintained at the Lawrence Berkeley Laboratories.

Table of Nuclides - Compiled at the Korean Atomic Energy Research Institute.

CRC Handbook of Chemistry and Physics - The 88th edition of the classic handbook of physical and chemical properties.

Encyclopedia of Mathematical Physics

Optics Encyclopedia

HyperPhysics - A free online resource covering most topics in physics, maintained at Georgia State University.

Weisstein's World of Physics - A free online encyclopedia covering many fields in physics and astrophysics, maintained by Wolfram Research.

Encyclopedia of Applied Physics - QC5.E543 1991

Graduate Programs in Physics, Astronomy, and Related Fields - QC30.A5125a

AIP Physics Desk Reference - QC61.P49 2003

Springer Handbook of Atomic, Molecular, and Optical Physics - QC173.S66 2006

Encyclopedia of Condensed Matter Physics - QC173.454.E53 2005

Springer Handbook of Condensed Matter and Materials Data - QC173.454.S67 2005

Handbook of Optics - QC369.H35 1995 (also online through knovel)