It's worth repeating: know what you're doing. Things you may have promised your readers include...
Your characters not only save the day, they do it without compromising their honor and it's a solution that will hold for the forseeable future. They deserve a standing ovation and celebratory beverages all around.
What He Deserved
You've inflicted a particularly awful villain on your characters and your readers want him to come to a particularly awful end. For example, what happened to Burke (the slimy, evil corporate rep) in Aliens.
However bad it might be, that question hanging over the story needs an answer. Hazy answers are not answers, they're new questions. Stories built on mystery (Twin Peaks, X-Files, Lost, etc.) tend to dodge these and some stories (The Blair Witch Project, etc.) can get away with dodgy answers. (What is the Blair Witch? Dangerous.) If you have multiple questions, you don't have to answer them all. But if you answer none of them... you've told the reader you can't be trusted.
OTOH, many mystery-based stories fall apart when they try to answer their questions. But they also cannot continue to not answer them. It's a catch-22. See: Twin Peaks, X-Files, Blair Witch, Lost...
Maybe you have two characters who've been on a collision course throughout the story. Often, it's the protagonist and antagonist, but it can also be two characters on the same team. If it's the latter, this often manifests as a fight for the alpha position in whatever group your characters have formed.
Or, if you're writing a love triangle, it's centered on the romantic lead. (note to self: how about a triangle of one guy and two women?)
Showdowns come in many shapes and sizes, from elaborate combat sequences to purely psychological duels where a few words set off a chain reaction that results in utter defeat. The genre you're working in and the premises you've set up have a huge influence in your reader's expectations, here.
Finally, a Kiss
If you've been teasing your readers with a relationship, you've promised them at least one major step towards romance. Those major steps being: a kiss, a confirmation that the other party is interested, a first sexual encounter, a clear sign of commitment, or you can go all the way to wedding bells and happily-ever-after. Or, if you want to be different, you've promised them a definite, final "no" to the relationship.
I am wrapping up the raw draft of Disciple, Part IV -- not quite a first draft yet -- and this has been weighing on my mind. What have you promised your readers?