If weekend estimates are accurate, Avatar is the box office champ for the third consecutive week, raking in an impressive post-holiday $68 million in domestic ticket sales. That puts its three week haul at $352 million and in 15th place on the highest grossing movies list. Now the “will it beat out The Dark Knight and Titanic” money watch will begin in earnest. It would be interesting if it took 12 years and another James Cameron film to best Titanic’s …