Other
Spacetech's Orrery: Comets Visitors From Afar
This site provides a report on comets, with many links to more detailed information. Content includes a focus on Halley's Comet, Hale Bopp, and Shoemaker-Levy 9.
NASA
Nasa Space Science Data Archive: Comet Fact Sheet
This comet fact sheet, supplied by the NSSDC, provides a table of information on selected comets, complete with commentary when appropriate. Includes details of missions to observe these comets.