CNBC is running a little slideshow of the 15 Most Profitable Movies of All Time. It's pretty interesting because these aren't necessarily the movies that made the most money, it's the ones that had the best ROI. I won't spoil the ending except to say that the most profitable movie returned 6150% of its cost.
Caveats - no one ever reports their real budget, so the whole list is a pack of lies. And they're all American figures, which strikes me as a little suspicious. Still the general contours - seems likely.