IAU: Minor Planet Center
The official body that deals with astrometric observations, and orbits of minor planets, asteroids, and comets.
http://cfa-www.harvard.edu/cfa/ps/mpc.html

Clementine Image Browser
Data server from the Clementine space mission. Contains images, search tool, time-lines, and mail.
http://clementine.cnes.fr/index.en.html

National Space Science Data Center
Provides access to a wide variety of astrophysics, space physics, solar physics, lunar, and planetary data from NASA space flight missions, in addition to selected other data, models, and software.
http://nssdc.gsfc.nasa.gov/

PDS - Planetary Data System
Solar system exploration science data archive, maintained at JPL.
http://pds.jpl.nasa.gov/

NASA's Marshall Space Flight Center
Specializes in development of advanced earth-to-orbit and space propulsion systems, and technologies.
http://www1.msfc.nasa.gov/NEWMSFC/