In this hilarious cult film and instant classic, Neil Patrick Harris plays himself and causes a whole lot of trouble for the main characters. Of course, the role is over-the-top, and he’s not really like that – or so we hope! Still, the cameo is hysterical and further adds to a great comedy film.
The movie and NPH’s cameo was such a hit they invited him back to be in “A Very Harold & Kumar 3D Christmas” in 2011.
Johnny Depp: 21 Jump Street
A-lister Johnny Depp pops up at the end of “21 Jump Street,” in a surprise reveal, where we learn that he is an undercover police officer. Of course, the fact that he played one of the main characters on the show version makes the appearance that much more amazing.
Interestingly enough, he isn’t credited in the film. The actor does have a thing for playing strange, out-there roles. Just look at “Edward Scissorhands” or “Sweeney Todd!”
Cameron Diaz: Minority Report
In the early 2000s, Cameron Diaz was a huge star, thanks to being in hits like "Charlie's Angels" and "There's Something About Mary" a few years before. She happened to be visiting the set of "Minority Report" in the midst of filming and ended up playing a small part of a businesswoman talking on a cell phone.
You may notice her in the scene where Tom Cruise is on the train, and a stranger looks up at him, eyeing him with suspicion.
Leonardo DiCaprio: Roseanne
Roseanne was another popular comedy that featured a lot of stars playing guest roles. Leonardo DiCaprio appeared in one 1991 episode before he became a household name.
The episode is titled Home-Ec, and the young future star plays a classmate of Darlene in what was essentially an extra role. Who knew DiCaprio would go on to become a superstar in Tinsel Town?
Ian Brown: Harry Potter and the Prisoner of Azkaban
The British musician, and the lead singer of the musical group Stone Roses, got to step into the magical world of “Harry Potter” when he played a wizard in 2004’s installment of the popular franchise.
He can be seen sitting in the Leaky Cauldron, reading a book about time, perhaps because he's a time traveler?