JMARS "JMARS (Java Mission-planning and Analysis for Remote Sensing) is a Java-based geospatial information system developed by the Mars Space Flight Facility at Arizona State University. It is currently used for mission planning and scientific data analysis by several NASA missions, including Mars Odyssey, Mars Reconnaissance Orbiter and the Lunar Reconnaissance Orbiter."
Gazetteer of Planetary Nomenclature - from the Internation Astronomical Union Working Group for Planetary System Nomenclature (WGPSN).
Physical Measurement Laboratory (NIST - National Institute of Standards and Technology) Physical reference databases are avaiable from NIST, including Elemental Data Index, Periodic Table Atomic Properties, Physical Constants, Atomic Spectroscopy Data, Molecular Spectroscopic Data, Atomic and Molecular Data, X-Ray and Gamma-Ray Data, Radiation Dosimetry Data, Nuclear Physics Data, and Condensed Matter Physics Data.
SAO/NASA Astrophysics Data System (ADS) - "is a Digital Library portal for researchers in Astronomy and Physics, operated by the Smithsonian Astrophysical Observatory (SAO) under a NASA grant."
NASA Lunar and Planetary Science - Fact sheets, mission information, images, and data for the planets, asteroids, and comets.