There is a wonderful part of The Camelot Project at the University of Rochester; it's an article about
The Questing Beast. There's a background essay, with seven different illustrations in the gallery. Here are my two favorites from that gallery, and you can also learn more at
Wikipedia.
Arthur Rackham, from T
he Romance of King Arthur and His Knights of the Round Table (1917)
H. J. Ford, from
The Book of Romance (1902)