Reddit top rated comments...
Any movie you watched back as a kid and haven't seen in years.
Snatch - It's a generic heist movie on the surface, but watching a second time really brings a whole new take to the movie.
Spartacus. I have seen that movie a dozen times, still no idea who the real Spartacus is. That's what's makes it a classic who-done-it.
Primer. That movie is crazy confusing.
Memento, Usual Suspects...
Airplane! Just watch it twice. Maybe 30 times
Eternal Sunshine of the Spotless Mind
The Prestige is great for this. They tell you at the beginning of the movie that the secret to a magic trick is always right in front of you. Then they spend the whole movie performing a trick that you still don't understand until the end of the movie. Upon a second watching, you see all the clues as they happen.
Synecdoche, New York
Fight Club and Arlington Road
Being John Malkovich