Well the AFI list was "top 100 movies of all time" so it could be of any timeframe
I've seen all of these, because I'm on a quest to see all 100 and started from the top. I had seen all of them except Citizen Kane - so I got the DVD for that and saw it.
Out of these I *love* Casablanca and have seen it many, many times. I think it's just brilliant - great dialogue, great acting, great lighting of scenes.
I'm also very fond of the Godfather series. I've seen that a few times. Third would probably be Gone with the Wind.