Wikimedia
Wikipedia: Comet
A nice encyclopedia article from Wikipedia on comets describes what they are, their physical characteristics, gives a history of comet study, and provides a list of well-known comets.
Other
Cometography.com: C/1995 01 (Hale Bopp)
This site provides a detailed overview of the comet C/1995 01 (Hale-Bopp), the great comet of 1997. Content includes discovery, and observational and orbit information, as well as several images.
NASA
Nasa: Comet Hale Bopp Images
This site contains 5,161 images of the Hale-Bopp comet from 1995 to 2000. This incredible photo archive is definitely worth a visit.
PBS
Nova: Doomsday Asteroid Hale Bopp & Hyakutake
NOVA provides a report on comet Hale-Bopp and comet Hyakutake. Content includes discovery and observational information.
Curated OER
Nasa: Space Place: Comet Hale Bopp
Comet Hale-Bopp's white dust tail and bright blue ion tail is visible from Earth.