Slate documents Governor Dean's flip-flops. (Slate incorrectly describes flip-flopping as two distinct actions: the original opinion as a "flip" and the change in opinion as the "flop". I've always conceptualized the flip-flop as only one action, being the changing of opinion usually, as seen in the second reference, as being a cynical attempt to follow political opinion.)

There are two references to "flip-flops" or "flip-flopping" on the Simpsons that I can think of. The first is when Sideshow Bob is running for mayor of Springfield.

Bob: Young friends, my opponent, Joe Quimby, is confused about your school system. Do you know what he does? He flip-flops.
[does backflips; children marvel]
Sometimes he doesn't know whether he's coming or going.
[walks funny, pointing in both directions; children clap and cheer]
He wants to sell your future short.
[shrinks, walks sideways; children clap more]

The second is Diamond Joe Quimby admitedly flip-flopping in front of a gathered crowd. This after finding out that Bart had fooled Springfield into believing he was a little boy named Timmy O'Toole trapped in a well, and then fell into the well himself:

Ever since I called for the rescue of that Simpson lad, I have taken a lot of heat. So, I am flip-flopping! I say, let him stay down there!