Forbes Magazine has placed Emma Watson 16th on its list of "The 20 Top-Earning Young Superstars." According to them, Emma made around $4M per Harry Potter movie.

From Forbes:
Her coy suggestions to the press two years ago that she may need a break from the Harry Potter film franchise, in which she plays Hermione Granger, no doubt sent Warner Brothers into convulsions. For the last three flicks, including last summer's Order of the Phoenix, she scored a substantial raise, earning an estimated $4 million per film. In July she confessed to Parade magazine that she has enough money now to never work again, adding, “but I would never want that."

Source: Forbes