I came across this thought...

Which film do you feel represents each decade of the 20th century the best?

This film does not neccesarily have to be made in the decade it is representing, the story just has to be set there. I would score this on terms of attention to detail, the look and style of the film, the dialogue, anything pertaining to setting the story in the given decade.

Here are my picks for some of them.

90's - American Beauty
80's - Thief/The Breakfast Club
70's - Boogie Nights
60's - The Graduate/Dr. Strangelove
50's - The Godfather Pt II
40's - The Godfather
30's - Citizen Kane/Chinatown
20's - Miller's Crossing/The Godfather Pt II
10's - Titanic
00's - The Godfather Pt II