Lynda was looking for humor in art. Have you checked out the parodies
of famous art? This seems to be a good impetus for students to get
started looking for artworks.
Once you start looking for them, you will see many examples of famous art
works used for advertisements. I've been collecting these for a number
of years now; other teachers and our librarian bring them in for me,
also. Of course, there will be many Mona Lisas, but there are also a
surprising number of The Thinker (even a Time magazine cover of a
chimpanzee in the same pose), Madame X, The Creation of Adam, and Henry
VIII. Charles Schulz has done a lot of them for the Metropolitan Life
insurance company; my favorite of those is Snoopy as Holbein's Henry VIII
("Snoopus Rex"). These make fun starting points for the students to
create their own, which, as Linda pointed out, are hilarious.