James Cameron's Avatar has done what seemed impossible, and is now the highest grossing film of all time worldwide (not adjusted for inflation). This is after a mere 6 weeks in theatres, and with no end in sight at this time.
Avatar's total domestic gross looks like it'll come in around $750 Million (it has amassed $555 Million so far, rapidly approaching Titanic's $600 Million domestic total), and as much as $2 Billion overseas. If the current pace continues, Avatar could gross as much as $3 Billion globally, making it the highest grossing film of all time regardless of whether inflation is taken into consideration.
Adjusted for inflation, Avatar's domestic gross is currently 26th, and if the $750 Million projection above comes true, it will land at #11 on the all-time domestic grosses, adjusted for inflation.
When ticket price increases are taken into consideration, the most attended film of all time in domestic terms remains 1939's Gone With the Wind, which grossed an estimated $1.5 Billion in domestic tickets sales over the course of several releases. Of course Gone With the Wind didn't have to contend with television, video games, or any of the other multitudes of entertainment available to audiences today. Globally, the world has not seen anything like Avatar since Titanic in 1997.