It's always fun to rank things, so here goes:
Top Five Fantasy writers:
5) Jonathan Bellairs (admittedly they are kids books, but the Johnny Dixon books are especially good. The Curse of the Blue Figurine, The Mummy, the Will, and the Crypt, The Eyes of the Killer Robot, The Spell of the Sorcerer's Skull, and The Chessmen of Doom are all delightful books.)
4) Robert E. Howard (especially his Conan stories)
3) Robert Jordan (though I do wish that the WOT was shorter by 3 or 4 volumes, with some editing out of the needless repetition that is an inadequate substitution for real characterization)
2) Tad Williams (especially his Osten Ard books, no one describes setting as lyrically or as well as Tad)
1) Steven Erickson (he does like his diatribes, but for the most part he's a keen observer and long form griping has never been written better or been dressed in better fantastical symbolism. Populating his book with villains that are incarnations of the worst attributes of humanity is nothing short of brilliant. Truly the Jonathan Swift of High Fantasy. It's always satisfying when these villains get their come-uppances.)
Top 5 Science Fiction writers:
5) Roger Zelazny (especially the first 5 books of the Chronicles of Amber, Jack of Shadows and Lord of Light is one of the best Sci-fi books ever written.)
4)Robert A. Heinlein (especially his short stories and novellas, the short story They and novella The Strange Profession of Jonathan Hoag are some of the best short form fiction around)
3) Jules Verne (sure it's laughable now to think that you could get humans to the moon using a giant cannon, but most of his work holds up remarkably well as plausible speculative fiction over 150 years after he wrote it, like Journey to the Center of the Earth, 20,000 Leagues under the sea and especially Dr. Jekyll and Mr. Hyde)
2) HG Wells (though his novels do have some skimmable parts, his prose is compact, his imagination vast, and his short stories are some of the best. His two volume Outline of History is fantastic as well, and it's commonly available at thrift stores.)
1) Horse lover Fats, aka Philip K Dick (if you've ever had a desire to peel back the veil of mundane reality and see the schizophrenic steel and wire machinery that keeps the happy suburban simulacrum of normal life humming, then strap yourself in and go through The Martian Times slip with Phil as your guide, and thrill to the gubbish delight of time traveling precogs used for lucrative building speculation. Or maybe you too can experience the enlightenment of subconscious thought manipulation through orthogonal time achieved by the blast right between your eyes of an intergalactic pink space laser, or perhaps you just want to fend off the unraveling of reality with a can of aerosol propelled Ubik. I highly recommend, with my highest commendation, The Exegesis of Philip K. Dick. It's a vast and strange and strangely vast world my friends.)
Top 10 Authors (a bunch of obscure ones here, I kid)
10) Friedrich Nietzche (The Birth of Tragedy/The Geanology of Morals, Beyond Good and Evil, Ecce Homo, and Thus Spoke Zarathustra are the fun books in philosophy to read. His language is ultra romantic and so very good, his criticisms are always stinging, and his ideas are always interesting. Though his conclusions are often misguided, the journey up the mountain with him is always fun).
9) Goethe (Faust parts 1 and 2)
8) Samuel Taylor Coleridge (He's my favorite poet and The Rhyme of the Ancient Mariner and Khubla Khan are my two favorite poems)
7) Gustave Flaubert (Salammbo is one of the 5 best books I've read. His three tales book, with the three long short stories (or short novellas if you prefer) A Simple Heart, St. Julian the Hospitaler, and Herodias, is one of my 10 favorite books of all times)
6) Herman Hesse (Steppenwolf has its moments, but for my money his best books are Siddhartha and Demian)
5) Haruki Murakami (this is definitely for the more mature readers, some very adult themes are dealt with, but the writing is superb, and there's just a tastefully modest dash of magical realism in his work. I highly recommend Hard Boiled Wonderland/End of the World, The Wind-up Bird Chronicle, and Kafka by the Shore)
4) Philip K. Dick (the only author that makes two lists. His short stories are some of the very best, but most of his novels are exceptional as well. Do yourself a favor and read Flow My Tears the Policeman Said, Through a Scanner Darkly, Ubik, Martian Timeslip, the Valis trilogy, and Do Androids Dream of Electric Sheep. You won't regret it, and if you crack under the psychic strain of realizing everything is gubbish, you'll still have lots to think about in your padded cell. I kid, it's really good stuff.)
3) Plutarch (everyone should read his Lives of the Noble Grecians and Roman's. Since this is available for free on Project Gutenberg there's no reason not to. The 4 volume set translated by Aubrey Stewart and George Long is much clearer in it's exposition, but the single file Collection is the AC Clough edited version of the John Dryden translation, which if you can adjust to reading it's rather elliptical cadence, you will be rewarded with some profoundly beautiful passages.)
2) Dostoevsky (Everyone is entitled to their opinion, but it's an undeniable fact that The Brothers Karamazov is the best book ever written. If you want to read a lesser known book by Fyodor, The Possessed is also amazingly good.)
1) George Orwell (Everyone knows 1984 and Animal Farm, but Orwell's lesser know books are just as good. Down and Out in Paris and London, Burmese Days and especially Keep the Aspidistra Flying are just as good. There's a four volume set of his collected essays and letters that is without a doubt the best thing I've ever read.)