The following are the most commonly used astronomical data resources. For other options, try here:
NASA Astrophysics Data System (ADS)
Provides over 620,000 abstracts from thousands of journal and conference sources. 1975-Present. Points to the full text in many instances. As of October 2001, includes over 6 million references from journal and conference papers. Also shows the number of citations to each paper.
SIMBAD Astronomical Database
Sets of identifications, measurements, and bibliography for astronomical data
Sponsored by the Centre de Donnâees astronomiques de Strasbourg (CDS), This is the most complete library of published astronomical catalogues and data tables available. One can find information contained in over 3,000 astronomical catalogs.
NASA/IPAC Extragalactic Database (NED)
Provides identifications, positions, photomatry, redshifts, and bibliography of extragalactic objects for which cross-identifications of names have been established. NED also includes images from 2MASS, from the literature, and from the Digitized Sky Survey.
NASA/Planetary Data System (PDS)
Archives and provides access to scientific data collected from NASA planetary missions, astronomical observations, and laboratory measurements.