What We Have to Lose
A wonderful collection of links to conservation organizations worldwide, and a rich resource of information about particular species. Contains, for example, the Smithsonian's MAMMALIAN SPECIES OF THE WORLD, a taxonomic hierarchy of all 4,629 currently recognized mammal species. See also http://www.wcmc.org.uk/.

Our Biological Resources
The USGS database of biological resources, maintained by Cornell University. Lots of good links on this NATIONAL BIOLOGICAL INFORMATION INFRASTRUCTURE homepage.

Measuring Biodiversity
A site devoted to assessing the distribution of highly valued terrestrial biodiversity and assigning conservation priorities.