The Bishop's Wife (1947)

So how can you go wrong with David Niven and Cary Grant? The answer is you can't, at least not in this movie.  Niven plays Bishop Henry Brougham, who prayed to God for the money for a new cathedral and is neglecting his family in his pursuit of a bigger better cathedral. So God sends Dudley (Grant) in order to teach Brougham a little Christmas spirit. The two of them instantly clash especially since Dudley starts to fall a little bit in love with Brougham's wife Julia. The story is a great one and was actually remade in 1996 as the Preacher's Wife. One interesting fact is that originally Grant was cast as Brougham and Niven was the angel, but Grant asked that the roles be switched. The result is pure magic.