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I guess it's too tricky to accurately adjust these things for inflation, but according to most such attempts, Gone With The Wind (above) is #1, and Star Wars is #2. In fact, Dark Knight isn't even in the Top 40 (yet).
When I was a kid, blockbusters like Star Wars, E.T., and Jaws played in first-run theaters for over a year, and people went back to see them again and again. These days, a year is enough time for a movie to hit DVD, HBO, and be long forgotten. (Dark Knight will probably be on DVD within six months.)
They just don't make "highest grossing films" like they used to.