In the movie Green Lantern, actress Blake Lively wears a Hamilton Khaki King Auto Chrono (modelnr. #H64616131).

This automatic watch from the Khaki Field collection has a metal strap and stainless steel 42mm case and features a chronograph and day/date display. The watch, with its 42mm quite a large watch for a woman, is from Hamilton's Gents' Collection.

This watch can be found on eBay and Amazon for around $925.

Thanks to amarett0 for the ID

Hamilton watches can be spotted in many movies, see a selection here.