Groundhog Day
It's hard to pick which collaboration between Harold Ramis and Bill Murray is the best, but Groundhog Day certainly stands apart from the rest of the pack for many reasons. Unfortunately, this film is also why these two comedy titans stopped speaking to one another for two decades.
They each had their own ideas about what sort of movie they were trying to make and although that's typically a recipe for disaster, whatever push-and-pull was taking place behind the scenes somehow helped transform this into a true classic.
Topics include: an attempt at a more studio-friendly version of the script where all of the story's wonderful mysteries were explained away, other actors considered for the lead role, how this film led to an entire sub-genre of similar fare, little details buried in the background of certain scenes, how long Phil was actually trapped in this town, and much much more!