Through the years I have read hundreds of books, and i have noticed that I see less and less stories that end without a happy resolution. i recently went back and read 1984 and I am Legend, While these were amazing books, neither one of them would have what I would call a happy ending. I can't be the only one who liked this style of writing, i just can't seem to find any current stories like this.
You might like Chuck Palahniuk books then. Twisted stuff and very few happy endings.
A couple of Heinlein novels come to mind: Podkayne of Mars and Glory Road. The release I own of Podkayne has the original ending an an alternate, which can hardly be called, "happy." Glory Road may be a touch more upbeat, though considering what Oscar Gordon is forced to confront after he supposedly wins the day, I wouldn't call it fully a happy ending. Heinlein's Moon is a Harsh Mistress has more of a "life goes on" ending to it, though it has serious losses among its leading cast.
And thinking of downright downer endings, Huxley's Brave New World is right up there, now that I think about it.
I prefer a "happy ending" but not at the cost of character development or plot. You see a lot of movies in paticular with a happy ending tacked on, and its just so annoying.