PBS
Pbs Nova: The Mysterious Life of Caves
Companion to a PBS program in the Nova series. There are wonderful photos of the Lechuguilla cave system in New Mexico, and some new information on how caves are formed.
Other
Glossary of Speleological and Caving Terms
This site features a glossary of speleological and caving terms. This resource is easy to use and gives a an adequate definition for each.