1 Avatar
2 Titanic
3 Marvel's The Avengers
4 Harry Potter and the Deathly Hallows Part 2
5 Frozen
6 Iron Man 3
7 Transformers: Dark of the Moon
8 The Lord of the Rings: The Return of the King
9 Skyfall
10 The Dark Knight Rises
Others?
Top will always be Gone With The Wind when inflation is adjusted, but I'd take Titanic as a solid #1 since it was a 90s movie pre-3D prices that pushed a lot of scope and scale in filmmaking.