Dean Winchester's 1967 Chevrolet Impala is a major character in Supernatural. Known as Baby, the car has carried the Winchesters through countless encounters with demons, ghosts, angels, you name it.
Dean Winchester lives in an alternate reality in My Heart Will Go On and drives a 1960s Ford Mustang. The car switch was a result of him saving the Titanic from sinking, which is probably very confusing to people who don't watch the show.