BiologyWise
Biology Wise: Classification of Animals
The classification system for animals is explained and examples given. Includes suggestions for how to teach the system to younger students and how to create a classification chart of the animal kingdom.
The Franklin Institute
The Franklin Institute: Living Things Families
What do centipedes and crabs have in common? What's so special about a backbone? Check this site out from The Franklin Institute if you are interested in biology and classification.