Be warned, if you haven't seen Disney's Big Hero 6, or if you simply didn't stay past the credits, there will be spoilers for a surprise cameo, so read on at your own risk. While this scene doesn't exactly spoil the main narrative drive of Big Hero 6, it wasn't included in any of the press screenings. It does, however, potentially set up a sequel, so you may want to check out Big Hero 6 in theaters first before reading on.
Big Hero 6 is Disney's first animated adaptation of a Marvel comic book, although it didn't have nearly the same amount of name recognition as a hit titles such as Marvel's The Avengers. Still, Disney managed to keep a Marvel tradition alive at the end of Big Hero 6, by giving comic book legend Stan Lee a voice cameo during an end credit scene.
The scene in question centers on T.J. Miller's Fred, whose family is always gone on their "secret island" during the movie. Fred comes home and looks at a family portrait, with his father bearing a striking resemblance to Stan Lee. When Fred touches the painting, it unlocks a secret room, and Fred's father, voiced by Stan Lee, reveals that both of Fred's parents are superheroes. While we don't see the entire end credits sequence below, we do get a glimpse at the animated version of Stan Lee, while the voice actor talks about his brief appearance.