A few nice extinct animals images I found:
Metridiochoerus hopwoodi - extinct wild pig - Smithsonian Museum of Natural History - 2012-05-17
Image by dctim1
Jawbone of a Metridiochoerus hopwoodi, an extinct giant warthog that lived in Africa. On display in the Smithsonian Museum of Natural History in Washington, D.C.
Metridiochoerus hopwoodi lived from 3.6 million years ago to about 117,000 years ago. It was about five feet long, and looked like a warthog. (Modern warthogs are three to five feet long, depending on species.) They were omnivores, eating both plant and animal matter.
They were commonly hunted by the ancestors of human beings.
Wild Animal Park 2007
Image by epochgraphics
Rare endangered white rhino. This is one of seven in the world and will be extinct in our lifetime...
Przewalski's Horse no longer extinct
Image by Transguyjay
Przewalski's Horse at Minnesota Zoo
This Mongolian horse was extinct in the wild, but Minnesota Zoo and other zoos helped to restore it to it's home.