Taxonomy

Encyclopedia of Life

http://eol.org/

Guide to the Animal Kingdom for Students and Educators

http://scientific.thomson.com/support/products/zr/ak-guide/

University of California Museum of Paleontology: Eukaryota (Systematics)

http://www.ucmp.berkeley.edu/alllife/eukaryotamm.html

ITIS: Integrated Taxonomic Information System

http://www.itis.gov/

The NCBI Taxonomy Homepage

http://www.ncbi.nlm.nih.gov/Taxonomy/