Here's a list, from the top of my head, of my favorite artists:
(http://www.art.com is a great place to look at many of these artist's work. ; ) )

Georgia O'Keefe
Ansel Adams
Wassily Kandinsky
Edgar Degas
Mary Cassatt
Jim Dine
Grant Wood
Winslow Homer
Andy Wahol
Salvidor Dali
M. C. Escher
Capser (http://www.betzgallery.com/all-products.php?fl=Q&sort=2a&page=2)
Van Gogh
Monet
Keith Haring
Matisse
Renoir
Cezanne