EOL.org is a collaborative encyclopedia project with the ambitious goal of documenting all species of life on earth. For those that wish to become involved, there is a section on how to become a curator for the species pages or submit photos, drawings and text to fill out their ever growing database. The species pages are rich with detailed photos and scientific facts.
Animalinfo.org is a modest looking gem of a site-- packed with carefully researched facts on dozens of rare or endangered animals, culled from highly credible sources.This is a great source of information and references especially if you're doing more serious research.
Leave it to the Wolverines to develop a great website on animals! Big plus on this site is the number and layout of the photos; gigantic plus: you can listen to lots of animal sounds. The individual animal pages are often pretty meaty, not geared for young kids. Well-documented with references and even cut-and-paste text for easy citation.
eNature.com is a very involved web resource for information on almost 6,000 species of wild animals and plants of the United States. There are lots of cool features here: like the mammal footprint and track identifier, animal mating call ringtones, a bird migration tracker and nature guides by zip code.
The National Aquarium in Baltimore offers pretty short and sweet fact pages for a relatively small but colorful variety of animals you don't commonly find on other sites, like the Grey-headed Flying Fox (from Australia), the Pygmy marmoset (from the Amazon River Basin), the Giant Amazon river turtle (from the Jersey shore), and the ever popular
Animal Fact Guide features articles about interesting and endangered animals from around the world.
About.com's collection of animal-related information, photos, videos, research, news and games provide a thorough resource for kids and adults, and also has links to some great animal-specific blogs.
The BBC's site has hundreds of animals in its database, from the usual cast of characters-- lions, tigers, bears-- to some less well known and more difficult to pronounce groups of creatures, like echinoderms (starfish, sea urchins, and other bottom dwelling invertebrates now you know).
Natureserve Explorer is the authoritative source encyclopedia on more than 70,000 plants, animals, and ecosystems of the United States and Canada. Explorer includes particularly in-depth coverage for rare and endangered species and a list of their numerous conservation projects.