I just read this online on The New York Times website talking about cars in movies.

"Andre Potten, administrator of the Internet Movie Cars Database, which tracks appearances by vehicles in films, says the most commonly seen movie vehicle appears to be the Ford Crown Victoria, because it plays well as both cop car and taxi."

http://www.nytimes.com/2008/05/08/movies/08hybr.html?_r=1&ref=movies&oref=slogin