I really like the Box Office Mojo website, it is jam-packed with pages and pages of interesting film information. I think the best section of the site is this:
All Time Worldwide Box Office Grosses
Currently James Cameron's Avatar from December last year (a film I really like) is number 1, with an incredible $2,730,200,000.00 in box office takings so far.
Other films I like which appear in the current top 10 are Pirates of the Caribbean with part 2 at number 4 and part 3 at number 8, Batman: The Dark Knight at number 6, and Harry Potter with part 1 at number 7, part 5 at number 9 and part 6 at number 10.