I'm assuming that a lot of folks on here are like me, and use The 13th Warrior as their go-to background noise while doing other things like cooking or laundry...
The Patriot and sometimes Cutthroat Island are the other movies that occasionally do that duty.
The Rocky Horror Picture Show is in its own category, as I've seen close to 400 showings in a theater alone, nevermind watching it on video. I used to perform with The RKO Army, the RI shadowcast, and was active on the national convention scene for almost eight years - I've seen the movie in twelve different US states and performed it in ten.
(Tangentially, the sequel, Shock Treatment is also something I've been involved in shadowcasting, and seen too many times to count.)
Other movies I've watched dozens of times, some of them more than one or two hundred times...
The Last Unicorn
Highlander
Ridley Scott's Legend, with Tom Cruise and Tim Curry
The Dark Crystal
Labyrinth
Willow
Bladerunner
Battle Beyond The Stars
the original Star Wars trilogy
Heavy Metal
300
The Boondock Saints
The League of Extraordinary Gentlemen
Ladyhawke
Spaceballs
Kingdom of Heaven
The Princess Bride
Gladiator
A Christmas Story
Blues Brothers
Gone in 60 Seconds
Braveheart
Beetlejuice
Shawshank Redemption
Clash of the Titans
Sin City
Krull
Goonies
Lost Boys
Big Trouble in Little China
Gremlins
Short Circuit
Johnny Dangerously
Conan the Barbarian
Master & Commander
the first three Indiana Jones films
Excalibur
Dragonslayer
Inception
Pitch Black
Watchmen
The Fifth Element
If I actually bothered to wander over to my huge dvd collection and actively consider it, I could easily rattle off at least a dozen more...