There's a listicle up on +Cracked
which is significantly more interesting than you may at first expect: 34 subplots that deserve their own movie. http://www.cracked.com/photoplasty_1462_34-fascinating-subplots-that-deserve-their-own-movie/
Why is this interesting? It's because it illustrates an important idea in good stories: when minor characters are developed beyond the level of faceless mooks or stock tropes, when they become interesting enough that you want to know more about them, the entire world and story become a lot richer.
I love running role-playing games, and one of my favorite things in running a game is to quickly generate NPC's with enough texture that they each become memorable. It turns out to be fairly easy to do this: the simple rule is that, the less screen time a character gets, the more vivid their idiosyncrasies have to be to stick in the memory. So the receptionist in the waiting room for the dead is this vividly colored character below; the guy selling you a horse has one eye, swears like a sailor, and has very strong opinions about his neighbor's butcher shop.
Note that these details were trivial to create; I've literally assembled tables of random personal characteristics, just to stimulate the imagination. (The great thing about an RPG is that if the side character proved interesting enough that it attracts the players' attention, you can then move them more and more front and center, and add nuance as needed; the cycle time of movies makes that not work as well there)
And seriously, an office comedy about the waiting room for the recently deceased in Beetlejuice?
I would totally watch that movie.