Throughout season one Johnny quotes Casablanca several times. One of the more popular ones is when he gives Jan a job in the last episode of the season and says "this may be the beginning of a beautiful friendship." Then shortly after he asks the piano player to play that song he likes.
The trivia item below may give away important plot points.
References The Sopranos early in Season 3 when Frank is shot, and moved into a room in the Hospital with a crazy old man. Frank hopes it's all a dream, the old man replies saying it is a dream and calls him Silvio, the character Steve played in The Sopranos.