Animal Diversity Web (University of Michigan Museum of Zoology)--has great pictures, too

Animal Bytes (SeaWorld/Busch Gardens)--has sounds, too

Animal Bytes (San Diego Zoo)

eNature

eSpecies Fact Sheet (Kidsplanet)

Critter Guide (PBS)

Critter Corner (Wisconsin Dept. of Natural Resources)

NatureWorks (New Hampshire Public Television)

Natural History Notebooks (Canadian Museum of Nature)

Wild Animals A to Z (Animal Planet/Discovery)

About Animals (Colorado State University)

Animals at the Center (Western North Carolina Nature Center)

Science & Nature: Animals (BBC)

Fantastic Animal Facts (FactMonster)

Lizards and Snakes Alive! (American Museum of Natural History)

Animals & Plants (Chesapeake Bay Program)