The Astrophysics Data System (ADS) is a NASA project, providing an abstract service, along with a subsidiary data service. Further to this, SUN/174, “An Astronomer’s Guide to On-line Bibliographic Databases and Information Services”, describes bibliographic and other resources of interest to astronomers.
SIMBAD is a ‘Set of Identifications, Measurements and Bibliography for Astronomical Data’. It’s a large database (5,416,970 objects in November 1998) of astronomical objects, which you can search by identifier, coordinates, or other sampling criteria. As well as basic data for the objects, it includes some observational data from, and journal references to, the object. You have to register before you can use it; it’s not free, but if you’re in the US or in an ESO or ESA member state, the costs are covered for you. Also at CDS is the CDS catalogue service, which allows you to search a list of almost 3000 catalogues, plus the contents of tables published in A&A.
If you’re using such catalogues, you might want to take a look at CAT, the Starlink “Catalogue and table manipulation library”, documented in SUN/181. This is a subroutine library for manipulating astronomical catalogues and similar tabular datasets. See also SUN/127, “The EXOSAT Database System”, and more generally SUN/162, “A Guide to Astronomical Catalogues, Databases and Archives available through Starlink”.