A terrific invertebrate diversity exploration based in the California Bay Area. The site has lots of excellent tools for identifying and learning about invertebrates, ideas for curricula, kids activities, and an 'ask an expert' link. Good site for kids and adults. (Insect identification tools are best for California, but there is lots of other information here too.)
Patuxent Bird Identification Info Center
Brief information on many species, with images, maps, and sometimes video. There's also a good glossary.
A wide variety of animals sounds.
A link to some whale sounds.
An online guide for North American mammal tracks.