Cave Art: 32,000 BC - 11,000 BC: Provides an illustrated article on the history of cave paintings on stamps.
Cave Paintings: A virtual museum of prehistoric art, with photographs and descriptions of artwork in Russia, Spain, France and South America. [Russian and English]
Chauvet-Pont-d'Arc Cave: Describes the discovery of this cave in France, with details of the research and images of the paintings. [English, French and Spanish]
Ice Age Art: A gallery of prehistoric art and sculpture, with a detailed essay and a Flash-based game to assemble and describe a cave painting.
Paintings, Engravings and Sculptures: Illustrated articles about famous cave paintings in France and rock engravings in Norway.
Pech Merle Prehistory Center: Illustrated descriptions of the wall paintings in this network of caves in France. [English and French]
The Cave of Lascaux: Interactive exploration of this prehistoric site, with illustrations of the artwork on its walls and roof. [English, French, German and Spanish]
Wikipedia: Cave Painting: Encyclopedia article describes the different discoveries and the conclusions that have been made about the people who created them.