Married couples in a movie.

[Zenge]

Cleopatra, Liz Taylor and Richard Burton. for one. although I dont believe they were actually married until after the film.

 

[Soo Sugar]

Cruise and Kidman in Eyes Wide Shut.
Clint Eastwood and Sondra Locke in dozens of movies in the late seventies and throughout the eighties (not married I know, but domestic partners for 15 years). the Outlaw Josey Wales was probably the best of the lot.
Pitt and Jolie in Mr and Mrs Smith (again, not married at the time, but got together while the film was being made).
Brad Pitt was also in a relationship with Gwyneth Paltrow while they were making Se7en together.
Val Kilmer and Joanne Whaley in Kill Me Again.
Gene Wilder and Gilda Radner in The Woman In Red and Haunted Honeymoon.
Steve Martin and Victoria Tennant in LA Story.
Sylvester Stallone and Brigitte Neilsen in Cobra.
Bruce Willis and Demi Moore in Mortal Thoughts.
Kurt Russell and Goldie Hawn in Overboard.

 

[Sydney]

IIRC, their relationship started during filming. I don't think they were a 'couple' when shooting began.

 

[AJD13]

Paul Bettany and Jennifer Connelly in Creation later this year.

 

[｡Tessa ｡]

david I read somewhere that Richard was having an affair with one of the dancers on the set of Cleopatra and Liz paid her off to get rid of her, whether true or not who knows....Tracy and Hepburn in Adams Rib

 

[SpockFan]

Lauren Bacall and "that old fella... what's his name? From the African Queen."

 

[Meg150]

Bogart


Lucille Ball and Desi Arnaz