National Geographic Magazine is all about Yellowstone National Park. The magazine's website has some excellent articles, videos, and interactive graphics about the animals and geology of the park. Unfortunately, about half of the resources on National Geographic Magazine's website are restricted to people who have paid for a subscription to the magazine. Here are some other free resources for learning about Yellowstone National Park.
PBS offers some excellent videos about Yellowstone. Return of the Wolves examines how and why wolves were reintroduced to Yellowstone and the effects of their reintroduction. The Volcano Under Yellowstone takes a look at the geology of the park including the famous geysers.
The USGS in partnership with the University of Utah produces the Yellowstone Volcano Observatory. The Yellowstone Volcano Observatory records and publishes data about volcanic activity in Yellowstone National Park. Much of the material on the site is very scientific in nature, but the Observatory website does offer some educational materials accessible to the non-scientist. The Yellowstone Volcano Observatory offers videos about the volcanoes of Yellowstone. The Observatory also offers photographic tours of Yellowstone.
Some other good resources for learning about Yellowstone National Park can be found in Google Earth. Turn on the National Geographic and Street View layers to some excellent images from within the park.
In March National Geographic published a great video containing remarkable footage of elk, pronghorn antelope, and mule deer migrations in Yellowstone National Park. The short video describes the length and direction of the migrations made by these beautiful animals. Make sure you turn up the volume to hear the sounds of the elk, mule deer, and pronghorn bleats.