Many artists have contributed to the Arthurian Literature through illustration. Here are some popular book illustrations, from the 19th century through contemporary graphic art.
There are several good, scholarly websites devoted to all things Arthurian, art as well as literature.
http://www.arthurian-legend.com/
http:/w.geocities.com/CapitolHill/4186/Arthur/htmlpages/kingarthur.html
http://www.marquettefiction.com/childrenofarthur/htdocs/KingArthurWebsites.html
http://www.lugodoc.demon.co.uk/MYTH/Arthur/Mal0.htm
Some of the most romantic of the Arthurian illustrations depict either King Arthur and Guenevere, or Lancelot and his lover, Queen Guenevere.