During the Credits (spoilers)
Halfway through the credits of Step Brothers, Brennan and Dale are shown landing a helicopter in the schoolyard where kids attacked them earlier in the movie. They get out and have an epic fight scene with all the kids. The extra scene last about four minutes and is one of the funniest scenes in the entire movie. After the fight is over Brennan and Dale are shown walking away talking, Dale asks Brennan if he played his drums and Brennan continues to deny it.
After the Credits (spoilers)
There is also a very short extra scene after the credits that shows Brennan and Dale getting out of bed, sleep walking and saying random things about passports and being late.