Tom Cruise as Ethan Hunt wears a Casio DW290-1V in the first Mission: Impossible (1996).

This Casio classic sports watch can be seen most clearly during the magic trick scene (watch here). Ethan still wears the watch during the meeting in London with Phelps.

UPDATE: the watch is out of production and can only be found on eBay! Get one while supplies last.

Shop at eBay ($55 - $68)
Used and new available

The Casio watch has a black case, a red line around the digital screen, and green text on the black case (Electro Luminiscence - Illuminator - Water Resist - 200m). Features include day/date, 5 alarms, stopwatch, light and hour signal. 

A cool feature is the Backlight that can be set to flash / light up during an alarm or hour signal.

Ethan Hunt also wears Casio watches in Mission: Impossible II (Casio G-Shock DW6900-1V) and Mission: Impossible III (Casio G-Shock MTG-910DJ). In Mission: Impossible Ghost Protocol, one of his colleagues wears a Casio G-Shock.