According to the Hollywood Reporter, RDJ is set to make around $50 million for his part in "The Avengers." Although the official number may not be known until years down the road, it factors in back-end compensation as well as box-office bonuses.
Downey Jr., who reprised the role of Tony Stark/Iron Man in "Avengers," has been the face of the Marvel Cinematic Universe ever since the first "Iron Man" debuted in 2008, so it makes sense that his payday is this high. (After the success of the first film, RDJ's agency renegotiated a deal after that would have the actor netting five to seven percent of Marvel's revenue from the movies he appeared as Stark.) As for Downey's superhero co-stars, they stand to make way less.
According to sources, Chris Hemsworth, Chris Evans, Jeremy Renner and Mark Ruffalo all signed paychecks in the $2-3 million range. Samuel L. Jackson and Scarlett Johansson will likely be paid somewhere between $4-$6 million.
As for the film itself, "The Avengers" is still bringing in huge box-office numbers, having grossed more than $1 billion in just 19 days.