"Please don't tell me how the story ends," - Kris Kristofferson
I've always preferred the limitless possibilities of beginnings to the concrete parameters that enclose most endings.
This feeling spans movies, television and especially books as there is nothing worse than a bad ending. Spending the duration of a novel with a group of characters who betray themselves or the fictional world they've inhabited at the conclusion is like a sucker punch to the kidneys and always leaves me feeling angry, disappointed or likely both at the same time.
"Angels and Demons" is a Dan Brown book that is a fine example of this problem. I am a sucker for ancient conspiracies and enjoyed the first half of the novel as a solid page-turner, but then Brown reached the end with a series of improbable events that turned out to be insulting to me as a human being. 
Consequently, his putrid ending spoiled the entire experience and I was pissed at myself for wasting time with the book, and at Brown for providing such an improbable climax.
The television show "Lost" recently announced it will end in 2010, an attempt to assuage fans who feared the series had no plans to wrap up and finish with any kind of dignity or answers to labyrinth of mysteries it has thrown at the audience since its inception.
I'm still not sure they have a satisfying ending up their sleeves, but I’m hoping that with 3 years to plan for one that they find a good answer.
The Lord of the Rings trilogy of movies concluded with "Return of the King," a film that refused to end as it kept tacking them on goodbyes, much to the chagrin of the audience. I actually enjoyed the multiple endings as it stayed fairly close to the actual books, but I understood the criticism from those whose asses were numb from sitting for 3 1/2 hours. 
More recently, "The Wedding Crashers" proved that flat-out stupid endings won't cause a movie to suffer at the box office. The finale of this comedy made no sense in the context of the film as the four main characters essentially throw their hands up, say we're regressing to our earlier role of wedding crashing and we'll just drive off into the sunset.
This ridiculous conclusion only worked because there were enough laughs preceding it that audiences were inclined to remember the hilarious shenanigans at the guest house rather than the shitbomb of an ending.
'Crashers' is most relevant to me right now because I’m 75 pages into a comedy screenplay, charging hard towards the finish line and yet I am still at a loss as to how to wrap up the loose ends and make a finale that works.
This is turning into a paralyzing factor in my writing, and nearly as frustrating as soft-core pornography. We'll see how it turns out, although I'm nearly ready to slap anything into place to be able to write "The End" at the bottom of the last page.
But then I think of Brown and many others who have butchered endings with sharpened steak knives and it's back to the drawing board because when you nail a conclusion that matches the initial wonder at some fictional world, then you've hit the bulls-eye.
The chances of missing it are large, but it's better to aim for the target than to simply shoot yourself in the foot.
-BDS
I call these "an then a miracle occurred endings" when clearly an author -TV/Movie/WhatEv, has no idea what to do. They are annoying. At least HEROES is giving it's viewers solid writing and a plot that was actually put together BEFORE the writing started. Novel (forgive the pun)idea.
so you found Crashers funny... to each his own...
When I read books I never read the end. The ends are always dissappointing. As for movies, same goes.
Video game endings are the worst. If I played that far into the game, I want to play more, the ending just means there's no more to play.
You could go the way of a Japanese horror flick and one of my favorite sayings..."then everybody died. The end."
Anonymous Boxer - I like all puns (no matter how good/bad/awful they are). Putting together a plot before starting to write/shoot/etc. is always a good idea, and should lead to less miracle endings or total bullshit ones.
WhatIgot - Crashers was funny until they left the beach/summer house. Then it got tedius and ridiculous. You could lump video games into the mix as well, but I don't think I've finished one out since The Legend of Zelda. That being said, I nailed that one.
Jlee - That's the logical conclusion of all stories if you take them far enough. Ha.
they never end movies well because they're always thinking- sequel sequel sequel.
True - it's all about the sequels in movies, but I still think churn out a decent ennding AND leave things open for a sequel. At least in theory.
I have just spent 2.5 of my day *today* faced with this same obstacle ~ an ending that does justice to the rest of the story. You have my sympathies! I do, however, think that one of the signs of a good writer is the realization that the ending must pack the same whollop (sp?) as the rest of the story and a writer who cheats frustrates me to no end. Anyone can slap "the end" at the bottom of a page (and we all have the temptation to do so at some point or another!) Congratulations on fighting this temptation and being a good writer.
So, I may be a good writer; I'm a lousy editor. That should read "2.5 HOURS"
Gack.
If you bring up Angel and Demons with me at a party, you will get a rant about the ending! I just see the title and I roll my eyes in disgust. I had so much trouble with the last 40 pages, and when I said something to one of my kids, he said "oh that's because the story's already over".... yeesh!! You'll find your ending, or maybe it will find you!
I've read ALL of Dan Brown's books. To each his own, eh? King is still the KING though..hands down.
Bostonpobble - Thanks for the good words and as I'm sure you realize, it can be a brutal slog to a decent ending. But it's worth fighting for - for now at least. Editing is another matter entirely.
Linda - The ending was an insult to me. I felt a personal affront at how blatantly stupid, dishonest and just plain bad it truly was and I can't believe anyone let it go into print that way (whether the story part was done or not).
Symplyamused - I liked The DaVinci Code just fine. And I found A & D to be pretty damn good until he starts having everybody pull a double-cross, leap from ridiculous heights and a few other asinine things that made the ending so awful for me. As for King, I love (LOVE) the Gunslinger series, but the ending left me a little angry as well.
from someone who is neither a good editor or writer: you've already put in most of the hard work (probably amounting to several months) why screw all that up by quickly slapping together a shit ending for the sake of saying "done".
I think everyone here is confident you'll put together an ending worthy of the rest of your screenplay even if it takes longer than anticipated.
by the way, everyone knows the only real appropriate ending to LOTR is sam and frodo deciding to brokeback it at the foot of mount gondor.
Ooooh, The Tower did end rather badly. I had to read it three times on last chapter to make sure I read it right. Clearly not one of his best endings. I think he was so tired of the story by then, he just winged it. Wait over 10 years for the story to finish and it falls flat..not good at all.
Idig - There was a lot of Hobbit homo-eroticism present in the movie (and the books), but I'm glad to see a little restraint as things could have gotten mighty shaky on Mount Doom. And I have no plans to slap a shit ending down (at least not yet), so I hope you're right something decent happening.
Symplyamused - Yep. It was pretty brutal, but a tremendous letdown for me. That being said, I thought that IT and The Stand both ended very well.