Lulu wanted to know what I thought were good sleeper movies. Her definition of a sleeper movie is a film that didn't get noticed at the box office, but is really good anyway, perhaps being noticed once it came out on video and has a word-of-mouth reputation for being really good.
I think many comedies fit in that category because traditionally, comedies are not given as much attention by critics, or the Academy Awards for that matter. A comedy sleeper I love is Nothing To Lose. It stars Martin Lawrence and Tim Robbins. Tim's character is not having a good day, and when Martin's character decides to rob him, the fun begins. The two are inseparable for the rest of the film, influencing each other and getting into silly situations. It's a definite laugh-out loud movie.
Then there's Election, which is one of Michael Moore's favorite movies. Starring Reese Witherspoon and Matthew Broderick, a high school election mirrors American politics in this hilarious R-rated film. Alexander Payne and Jim Taylor wrote the screenplay. You may recall they also wrote the screenplay for the film Sideways. Give them all a view. You won't fall asleep during these.