R. Scott Bakker's work is relatively new; his first novel, the beginning of the Prince of Nothing series, The Darkness that Comes Before, was first published in 2003, and since then he has written direct sequels The Warrior Prophet and The Thousandfold Thought, as well as a start to the second series within the same "Second Apocalypse" continuum The Judging Eye (which I have not yet read), and finally a standalone novel Neuropath. His series work is all fantasy, while his standalone novel is a mix of mostly horror and some science fiction.
His Second Apocalypse novels are really interesting to me. They are strongly realized, with a memorable setting and strong cast of characters. They are set in a series of events that bears some resemblence to the Crusades of medieval history. They are also quite interesting novels in terms of thoughts that they inspired in me, the sort of stimulation of mental processes described in the Apologia of this website. The titular "Prince of Nothing" character was very different from most fantasy protagonists, in that he was primarily a manipulator of others, something that Bakker managed to pull off and make believable. I thought that Bakker's use of the limited third person viewpoint with the characters worked out well. My only real complaint is that much of the writing is merely serviceable. Some of it is quite good, and it is never actively detrimental to the story, but it fails to shine occasionally.
Neuropath is mostly horror, and therefore ought not to be the provenance of this site. But it was quite well-written horror that I recommend to fans of that genre. At times it didn't work so well, but mostly it was quite horrifying but also fascinating.
Dan Simmons has written a number of books within the fantasy and science fiction genre. He has also written a few horror novels, and indeed horror themes tend to permeate sections of his other novels. He tends to include a lot of references to classic literature in his novels, including Keats, Twain, the Illiad, Shakespeare, etc. His best piece of fiction is Hyperion.
Hyperion is a science fiction novel about a series of pilgrims travelling, on the eve of a war, and choosing to tell their tales and reasons for travelling to one another as they go; this theme is purposefully borrowed from Chaucer's Canterbury Tales. It is quite interestingly written, and each of the protagonists has a distinct narrative style and voice. The universe of the book is fairly detailed in it's conception, and the characters are rock-solid. It is incomplete without it's sequel, The Fall of Hyperion, which provides closure and an ending for the first book. Unfortunately, the second book in the series is rather lacking compared to the first - there is a fair bit of extraneous scenes and things that really added very little to the overall narrative. They can be found together as Hyperion Cantos.
Related books Endymion and it's sequel The Rise of Endymion is a far more pedestrian sort of novel, with a general science fiction adventure plot. It was still interesting, and the characters and universe fairly well conceived, but at times it falls a bit flat compared to it's predecessors in the same universe. It is not a bad pair of novels, merely less interesting than it's predecessor.
Simmons has written kind of a lot of other fiction, some of it relevant to this site. Illium and Olympos are interesting but not as well written as earlier books, and Olympos in particular was a disappointment. They also suffered suspension of disbelief issues at times. The Fires of Eden is a sort of mixture of horror and fantasy, and was alright but never found much interest for some reason - possibly because some characters were little more than caricatures and the ending was anticlimactic. His work tends to vary in quality a lot - some of it is excellent, while some of it is poor.
Finally, Simmons Prayers to Broken Stones is a good short story collection; while some of his short stories are completely frivolous (see: Vanni Fucci is Alive and Well and Living in Hell), others are quite well written and more than a little disturbing (see: The River Styx Flows Upstream).