Here are a collection of Celestia, and space related links, which you may find useful.
Celestia:
http://216.231.48.101/celestia/ - Celestia's home page.
http://216.231.48.101/forum/ - Celestia forums.
Orbital elements etc:
http://ssd.jpl.nasa.gov/ - JPL's Solar System Dynamics index page. OR - go straight to:
http://ssd.jpl.nasa.gov/horizons.html - HORIZONS ephemeris service.
http://ssd.jpl.nasa.gov/dastcom.html - DASTCOM - Orbital elements for asteroids and comets.
Connect to HORIZONS telnet at ssd.jpl.nasa.gov port 6775
Or use HORIZONS e-mail method @ horizons@ssd.jpl.nasa.gov
http://cfa-www.cfa.harvard.edu/iau/mpc.html - Index of the Minor Planet Center's pages.
http://cfa-www.harvard.edu/iau/Headlines.html - Astronomical headlines from the Minor Planet Center. All new moon discoveries are announced here, and there are links to MPEC's where you can get more info on the discoveries
http://www.celestrak.com - Celestrak, from NORAD. Orbital elements for Earth orbiting satellites, the ISS, and the Space Shuttle. Includes archives of previous STS missions.
http://liftoff.msfc.nasa.gov/RealTime/Jtrack/3d/JTrack3D.html - J-Track 3D. View hundreds of Satellite orbits in real time 3D.
http://www.extrasolar.net/ - Extrasolar Visions. Orbital elements and other data for hundreds of Planets and other objects, orbiting around other stars.
http://www.johnstonsarchive.net/astro/asteroidmoons.html - A great page for details on Binary asteroids, and asteroids with moons, like Ida and Dactyl.
Textures:
http://planetscapes.com/maps/cylmaps.html - Planet & moon textures for most bodies in the solar sytem.
http://gw.marketingden.com/planets/planets.html - Realy good planet textures & bumpmaps for 9 planets & the moon (1k, 2k, 4k, 8k)
http://publish.uwo.ca/~pjstooke/plancart.htm AND http://www.psi.edu/pds/maps.html- Phil Stooke's great textures for asteroids and small moons (for Celestia use the cylindrical map option)- the first link's textures are mostly artistic, but the second's are more photo based.
http://hubblesite.org/ - Hubble space telescope image archives
http://visibleearth.nasa.gov/ - Hires earth textures
http://photojournal.jpl.nasa.gov/ - JPL's Planetary Photojournal. Thousands of the best images, of hundreds of Solar System bodies, Stars and Galaxies.
http://www.shatters.net/~t00fri/texfoundry.html - t00fri (Fridger Schrempp)'s Texture Foundry site. Brilliant Earth, Jupiter and red Mars Textures. Bumpmaps, textures, specmaps, and cloudmaps, in 2k, 4k and 8k.
Space mission sites:
http://galileo.jpl.nasa.gov - Galileo.
http://saturn.jpl.nasa.gov - Cassini-Huygens.
http://mars.jpl.nasa.gov - All Mars missions, including past and future planned missions.
http://deepimpact.jpl.nasa.gov - Deep Impact (Will impact comet Tempel 1 to see what's inside).
http://sirtf.caltech.edu/ - Space Infrared Telescope Facility
http://ulysses.jpl.nasa.gov/ - Ulysses Solar Polar mission
http://stardust.jpl.nasa.gov - Stardust
Add-ons and reference material:
http://bruckner.homelinux.net/celestia.html - Bruckner's Celestia Add-ons.
http://www.lns.cornell.edu/~seb/celestia/index.html - Selden's Celestia pages- everything is here- literally!!
http://www.la-guarida.com/Celestia/ - Praesepe's Celestia add-ons. Moon, ring, planet & nebula textures, & other stuff too. Really high quality!!
http://mikecelestia.to-j.com/index.htm - Mike's Celestia Add-ons. Some visitors outside the U.S. may have problems accessing this site. (But try anyway)
http://www.fsgregs.org - A selection of Sci-fi and other add-ons for celestia, by Frank Gregorio
http://ennui.shatters.net/~rassilon/ - Rassilon's Celestia Add-ons.
General Space Links:
http://www.nasa.gov/ - NASA's homepage. Also has one of the best Flash intros on the Internet, if you ask me.
http://www.esa.int - The European Space Agency. The sole reason French Guiana has the Euro...
http://www.space.com - Space.com. A great site for worldwide Space science, technology and mission news.
http://www.astronomy.com - Astronomy.com. Astronomy Magazine's website.
http://www.spaceflightnow.com - SpaceFlightNow.com. Similar in content to space.com, but much more in-depth coverage.