BBC Animals has videos, still photos, and extensive articles about wildlife for older kids.
National Geographic Creature Feature web site has video and audio of animals, as well as facts and maps of where they live.
National Geographic Kids animal page is easier to access, and contains great photos and video.
The Nature Conservancy has photos of animals arranged by habitat.
Rainforest at Night is also from National Geograhpic. The kids love it!
Smithsonian National Zoo Cams are very exciting to watch.