Someone has posted an absolute treasure trove of work by the great paleo artist and natural history illustrator Zdeněk Burian on Flickr!
The set is extensive and includes numerous paintings and many drawings of his range of subjects, including dinosaurs, flying reptiles, prehistoric mammals, undersea life, prehistoric plants, primates, early humans and portraits of famous naturalists. Many of the images are linked to large reproductions.
Yes, many of the reconstructions of prehistoric animals are inaccurate in light of recent findings, but Burian was, first and foremost, a terrific painter and draftsman.
Enjoy it while you can; resources like this have a tendency to be ephemeral.
See my previous post on Zdeněk Burian.