Inspec is the most comprehensive index of physics journal literature.
Scopus is the most comprehensive multi-disciplinary database of peer-reviewed literature. Also good for citation analysis.
SPIN, part of AIP's Scitation platform, searches every journal published by the American Institute of Phyiscis and affiliated organizations in Russia and the Ukraine. You can also search Scitation which is less oriented towards physics.
IOPscience searches every journal published by the Institute of Phyiscs.
arXiv is an open access e-print archive that is particularly strong in high energy physics. Falvey Memorial Library provides financial support for arXiv.
INSPIRE an open access high enery physics information system, including links to e-prints in arXiv.
ADS Astrophysics Data System is an abstract service.
PHYSICSnetBASE provides access to a growing collection of over 230 books from CRC Press and the Institute of Physics Publishers.
OpticsInfoBase contains all OSA journals and recent OSA conference proceedings.
Journal Citation Reports is the source for journal impact factors.