Wizard of Oz
The Wonderful Wizard of Oz is a book written by L. Frank Baum.
In "Selma's Choice," Homer and Bart sing part of the song "Ding-Dong, the Witch is Dead" from the movie.
In "Whacking Day," Kent Brockman teases a "where are they now"-type feature on the Munchkins from the movie (as part of a segment on "Eye On Springfield"), before a cut shot to a row of gravestones in a cemetery.
In "$pringfield (Or, How I Learned to Stop Worrying and Love Legalized Gambling)," Homer quotes the (incorrect) line from the movie about the sum of the square roots of any two sides of an isosceles triangle being equal to the square root of the remaining side. However, a random man corrects Homer.
In "Homer the Great," Homer announces he will follow the "yellow drip road," a reference to the yellow brick road from the book and movie.
In "Lisa's Wedding" in the future. there were lots of Tin Men walking and behind is Scarecrow and Cowardly Lion. but Dorothy, Toto, Munchkins, The Wizard, The Good Witches and the Wicked Witch of the West aren't seen.