Certainly China Miéville would qualify there. I myself am not a great fan, but that is more a matter of his work simply not quite appealing to me personally; I would nonetheless highly recommend him as one of those very much worth keeping an eye out for.
Moorcock's worlds sometimes use more traditional figures or tropes, but often in non-traditional ways; and tragedy is often the tone. Let's face it: when, in more than one instance, your Champion either destroys the earth or witnesses the destruction of the entire universe -- sometimes multiple universes -- you're not exactly dealing with the typical "happy ending". Often even when he wins, he loses. The general theme of Moorcock's work can be summed up in a quote which appears, in different forms, in several of his books: "The war, my friends, is ceaseless. The most we can expect in our lives are a few pauses in the struggle, a few moments of tranquillity. We must appreciate those moments while we have them."
A lot of fantasy would fit what you describe as "dark fantasy", including such a piece as H. Rider Haggard's She (which is something you should definitely look up) and no few of Lord Dunsany's writings.
You might also want to look up Storm Constantine's work, while you're at it....
And, of course, Smith's work very seldom features "happy endings"... though some of the darker ones do have a rather mordant humor to them. Robert E. Howard's fantasies also often have ambivalent to dark endings, and there is a rather grim tone to quite a few. (The Conan stories are probably among his lightest in this respect, though even there you have no few examples of his awareness of, as de Camp put it, "the underlying tragedy of life": "Beyond the Black River"; "Queen of the Black Coast", with its strikingly grim jest using the necklace of blood-colored stones; "The God in the Bowl"; "The Tower of the Elephant"; "A Witch Shall Be Born"; etc....)
