Ok I have an issue with the term "OLD MOVIES". My reason is if you haven't seen it it is new to you!
There are great films that belong in the lexicon of our collective culture. To Kill a Mockingbird is one of those films. I don't care what your social station, cultural background or political position this film speaks on so many levels and teaches us to be great human beings.
But I don't want to be too preachy here as I too like many different genres of film and all have value in some way. Even the turkeys!
Which if I still have it correctly the reigning worst film of all time still is Santa Claus Conquers the Martians. If you haven't seen it it is a grueling suspension of disbelief this film was ever made. It even has the first ever staring role of a 5 year old Pia Zadora!
I do see a lot of picks here that are what I would consider mainstream. I would offer the following as great films to see as well: