The Wriston Art Center Galleries Digital Collection at Lawrence University has over 1500 images of various artworks, focusing especially on prints & printmaking and ancient coins. All can be viewed in extremely high resolution (click "export image" above the artwork). Here are a few I particularly like: Beginning of Winter (Japanese woodcut), Rising Sun (Paul Klee painting), From Distant Lands (watercolor), Three Kings (Jacques Villon engraving), Untitled I (netting) and Noble Lady and Prince (Japanese woodcut).
Honoré Daumier is one of the great French artists of the 19th Century, beloved of no less an aesthetic judge than Baudelaire. Most famous as a lithographer and caricaturist, over 5000 of his lithographs and engravings can be seen, in high resolution, at The Daumier Register. One of the best places to start are the many online exhibits of his work.