This one will be brief, I promise. What do you mean my fingers are crossed behind my back? They are not!
Much.
Archetypes
Hate to break this to you, but there are only five story plots in all of fiction. That's right, five. But wait, you say, there are literally billions of billions of stories out there, how can there only be five plots? Because all of those stories are just different retellings of the Five Great Stories, or Archetypes. The details vary from tale to song, but the general structures are the same. The exceptions to this rule are existential stories without a plot, and stories about historical events or persons.
The usefulness of this becomes apparent when you're half-way through a story and aren't quite sure what should happen next. Knowing which archetype you're dealing with will assist you in finding which Point B your story should head for.
Archetype 1: Hero/Villain
This plot is the most used in all American fiction. It's good guy vs. bad guy. Harry Potter is of this Archetype. The Hero is brave and cunning, with a mysterious past and some sort of weapon that allows him, and only him, to defeat the Villain. The Villain is the opposite of the Hero, but has much the same abilities. The Villain generally has some past connection with the Hero, be it the slaughter of parents in Voldemort's case, or being the parent in Darth Vader's case.
The plot of a Hero/Villain story runs like this: The Hero is somehow called to action, sets out to beat the bad guy with many trials and discoveries on the way. At one point he looses hope or ability, then draws on his inner strength and defeats the Villain honorably, often despite the Villain's cheating. After defeating the Villain, he either dies or returns home to fanfare. Unless, of course, we're discussion Fitz in Robin Hobb's Assassin's Apprentice series or Bruce Wayne of Batman. In both those stories, the hero is left to rot with age and bitterness in his own secluded hideaway.
Archetype 2: Cinderella
Cinderella is what it sounds like: two people from disparate backgrounds meet, and after some confrontation or struggle, form an emotional attachment. About half-way through the tale, something drives them apart, either physically or emotionally, but they get back together at the end. The attachment doesn't have to be romantic, it could be friendship, family, or even just working together in peace. In quite a few Cinderella stories, the two protagonists face a common enemy. Cinderella can also form a sub-plot in a Hero/Villain story.
Archetype 3: Star-crossed
This archetype starts like a Cinderella story, but the separation is permanent.
Archetype 4: Mixed Identities
This story is best shown in The Prince and the Pauper. Someone is confused with someone else, and all hell breaks loose. The stories can be comedies like Switching Places or serious. Crime mysteries are Mixed Identity stories. At the end of the story, the mix-up is revealed. Often times the audience is aware of the mix-up but the characters are not.
Archetype 5: Slapstick
The best (and believe me, I cringe to use the word here) example of slapstick is Austin Powers. Slapstick is pure comedy that parodies one of the other plots, and sometimes forms a parody of a specific plot, as Austin Powers mocks James Bond. Done well it's awfully funny to read or write, done poorly it's a solid nightmare of stupidity. Slapstick, like alcohol, should only be used by those who know what they're doing and won't get hurt. Also like alcohol, too much is a terrible thing.
So, those are the five basic plots, the five roadmaps of storydom. You can certainly mess around with certain elements of each, and shock the spit out of your readers when you do. Have the villain win, make the Hero a small evil defeating a larger evil, change the fanfare to hate, have the mix-up not really be a mix-up - whatever strikes your fancy. Fiction, like dreams, is virtually without rules, and broken rules can be absolved via Explaination.