+5
Going to the movies:
The Last Picture Show (1971) - not really about movies, but has some drive-in movie scenes.
The Purple Rose of Cairo (1985)
Matinee (1993)
Movies about making movies or about the movie business:
Singin' In the Rain (1952)
Stardust Memories (1980)
Who Framed Roger Rabbit (1988)
The Player (1992)
Ed Wood (1994)
Gods And Monsters (1998)
For Your Consideration (2006)
Related:
The Three Amigos (1986), Galaxy Quest (1999) & Tropic Thunder (2008) all have a similar theme about movie actors thinking they are performing, but actually get into a real adventure that is similar to their movie roles!