The show is filmed entirely on the Universal Studios back lot in Hollywood. The town square is the same central place that was used in the Back to The Future trilogy. Subsequentially, Tom Wilson who played Biff Tannen has been known to pop up now and then in the show.
Cesar Millan (also known as the "Dog Whisperer"), has featured a couple of times in the Ghost Whisperer series. During the first season episode "Dead Man's Ridge", the character Andrea was twice seen reading a book written by him. Then in the second season episode "Children of Ghosts", Cesar makes a cameo appearance as himself.
Director John Gray is from Bay Ridge, Brooklyn originally and in many of the episodes there are references to streets and locations from Bay Ridge Brooklyn (example, Lento's Restaurant in the movie was the name of an actual Bay Ridge restaurant for over 30 years).