From Cornell Unviersity, "arXiv is an e-print service in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance and statistics."
The ComPADRE Digital Library is a network of free online resource collections supporting faculty, students, and teachers in Physics and Astronomy Education.
An open access site presenting 13 of the 14 volumes published to date by the editors of the Einstein Papers Project, covering the writings and correspondence of Albert Einstein (1879-1955) from his youth to 1923.
an open-access site for The Collected Papers of Albert Einstein, the ongoing publication of Einstein's massive written legacy comprising more than 30,000 unique documents
Includes data on fundamental physical constants, atomic and molecular spectroscopy, ionization cross sections, absorption of x-rays and gamma rays, radiation dosimetry, half-life measurements, atomic weights, and condensed matter physics.
Physics Central brought to you by the American Physical Society represents some 48,000 physicists, and most of the work centers on scientific meetings and publications.
