He's in them all. From teh Wiki:
In X-Men (2000), Lee appears as a hotdog vendor on the beach when Senator Kelly materializes naked onshore after escaping from Magneto.
In Spider-Man (2002), he appeared during Spider-Man's first battle with the Green Goblin, pulling a little girl away from falling debris.
In Daredevil (2003), the blind child, Matt Murdock, stops Lee from crossing the street and getting hit by a car.
In Hulk (2003), he appears walking alongside former TV-series Hulk Lou Ferrigno in an early scene, both as security guards at Bruce Banner's lab.
In Spider-Man 2 (2004), Lee again pulls an innocent person away from danger during Spider-Man's first battle with Doctor Octopus.
In Fantastic Four (2005), Lee appears for the first time as a character from the comics, in a role credited as Willie Lumpkin, the mail carrier who greets the Fantastic Four as they enter the Baxter Building elevator.
In X-Men: The Last Stand (2006), Lee and Chris Claremont appear as two of Jean Grey's neighbors in the opening scenes set 20 years ago. Lee, credited as "Waterhose man," is watering the lawn when Jean telekinetically lifts the water from the hose into the air.