Casio LTP1165A-1C - Thekla Reuten - The American
This simple but stylish Casio watch (with the Casio 1330 module) is water resistant, measures 32 x 21 x 7mm and weights 69 gram. The same model is available with a pink dial (color code 4C) or blue dial (color code 2C). A gold version, or black with chrystals on the 12 and 6 o'clock are also available, see slideshow below for an overview.
George Clooney wears a slightly more expensive watch in the same film, an Omega Speedmaster.
Thanks to sruzgar for the ID