This took me longer than I thought it would, but the one thing they have in common is that they all put on a lot of weight to play a specific role.

George Clooney, Syriana, 30 lb.
Charlize Theron, Monster, 30 lb.
Robert De Niro, Raging Bull, 60 lb.
Renee Zellweger, the Bridget Jones movies, 40 lb.
Sylvester Stallone, Cop Land, 40 lb.
Vincent D'Onofrio, Full Metal Jacket, 70 lb.
Russell Crowe, Body of Lies, 50 lb.