I'm not that big of movie person,but I think I'll have to agree with Mia on the Godfather.I've watched it many times over the years and I so love James Caan!There are a few others that I've probably watched more than Godfather...Dirty Dancing would be one of those,as is Pretty Woman.
I don't really have a favorite movie, one that I could watch over and over again. If I absolutely had to make a decision, I could go with The Lord of the Rings.