I have a pink Minnie antenna ball, the best way to find your car in a crowd, and a "WDW its where I want to be" sticker on my back window. I also have, and you didn't put this one in your poll, Mickey mouse seat covers! They are the coolest! My car is green so I lovingly refer to it as Elliot (as in Pete's Dragon).
At one point I bought a Mickey Mouse Walt Disney World Magnit to put on the back of my car, but when I went to put it on I realized that my whole car is made of plastic!
I did at one time have a license plate cover, but cops in my city have been going nuts writing tickets for "obscured license" to people who have these tips of things, so I just took it off to avoid a $200 fine.