Catalogue of Life
The Catalogue of Life is a comprehensive and authoritative index of the world's known species of animals, plants, fungi, and micro-organisms. Features include a detailed taxonomic tree that is browsable down to the species level. The Catalogue is compiled from information provided by taxonomic databases from around the world and holds information on the names, relationships, and distributions of over 1.5 million species.
National Center for Biotechnology Information (NCBI) Taxonomy Database
This NCBI database contains an extensive collection of taxonomic information on organisms. A search box is provided for access to information on individual organisms. This site also includes links to useful taxonomy resources.
Created by the Association of Biodiversity Information, this site provides access to information on more than 70,000 plants, animals, and ecosystems of the United States, Canada, and Latin America. Entries for organisms provide common name, scientific name, taxonomic hierarchy, distribution, conservation status, ecology and life history information, references, and more. NatureServe includes particularly in-depth coverage for rare and endangered species.
Tree of Life
The Tree of Life Web Project is a collaborative effort of biologists from around the world. The site provides pictures, text, and other information for organisms, living or extinct. Pages also contain hierarchical information in the form of an evolutionary tree of life.
Provided by the library at the Marine Biological Institute at the Woods Hole Oceanographic Institution, this site offers a comprehensive catalog of known names of living (and once-living) organisms. It includes classification information, synonyms, and common names.