With it's $31 million this weekend, Avatar passed the following films on the All Time Adjusted Box Office. (Which means inflation IS included.).
In order that it passed:
25.) Grease
24.) The Lion King
23.) Mary Poppins
22.) Forrest Gump
21.) The Godfather
Quite a impressive list of films to pass to overtake the #21 spot all time.
If it makes another $24 million, it will pass Fantasia for #20 on the list. For some perspective, Fantasia came out in 1941 although in a time where moviegoers went out in ridiculously high numbers compared to today.
It might make that before Friday, and if it does, these films are up next:
Adjusting for inflation isn't any more telling than not adjusting for inflation. As you said, movies like Gone with the Wind didn't have to compete with modern media, or piracy. Plus, most of the movies on that list were released multiple times, or were in theaters for years. Avatar has been in theaters for less than two months, and will soon drop drastically in its gross. Alice in Wonderland will take over the 3D screens as theaters are contractually obligated to show the movie in 3D, which means Avatar will lose its highest grossing line of revenue.