Pictures of Comets, NSSDC
http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-comets.html

Comet Hyakutake, The Great Comet Of 1999
http://www.jpl.nasa.gov/comet/hyakutake/

Comet Shoemaker-Levy 9 Impact On Jupiter
http://www.jpl.nasa.gov/sl9/

The Return of Comet Halley
http://www.astrosociety.org/education/publications/tnl/01/01.html

Minor Planet Center, Smithsonian Astrophysical Observatory
http://www.cfa.harvard.edu/iau/mpc.html

PDS Small Bodies Node: University of Maryland
http://pdssbn.astro.umd.edu/

Asteroids and Comets Page, NSSDC
http://nssdc.gsfc.nasa.gov/planetary/planets/asteroidpage.html

Comet Fact Sheet, NSSDC
http://nssdc.gsfc.nasa.gov/planetary/factsheet/cometfact.html

Frequently Asked Questions: Comets, Asteroids, Planets, NSSDC
http://nssdc.gsfc.nasa.gov/planetary/planetaryfaq.html