Diane Duane
She writes some truely wonderful sci-fi/fantasy novels, but that so totally fails to describe them. Her books are luminous, strikingly original, brilliantly written and, perhaps best of all in today's trend towards doom and despair, profoundly hopeful without being blindly so.
Reccomended reading:
So You Want to be A Wizard and
Deep Wizardry
In the Star Trek sub-genre,
Spock's World is probably the best, along with My Enemy, My
Ally and Doctor's Orders.
Also very, very good,
and in a class all their own, is the whole series of books starting with
The Door into Fire.
Edna St. Vincent Millay
She wrote great poetry that is now almost totally overlooked in most academic courses. We're talking as good as or better than T.S. Eliot, people. Her writing is strong, passionate, defiant, and exuberant in many places. I have rarely been more annoyed than I was the last time I came across a textbook deriding her work as "attempts to imitate Shakespeare". Huh? Okay, she wrote some (good) sonnets. She's _better_ than Shakespeare. More approachable, more original, more intense. Do yourself a favor. Read her poems.
Reccomended reading: just about anything, but most especially
Renasence, which is a longer poem, and The
Harp-Weaver, which is in the poetry collection of the same name, I
believe.
Robert A. Hienlen
The man is a very fun writer. He does this very lighthearted, hopeful/gritty sort of writing that I find very enjoyable. And, fortunately, he actually took the time to get most of the science right. When his characters start talking about "right-angled time", he'll back it up! This, now this is good Sci-Fi.
Reccomended reading:
The Number of The Beast and Time Enough for Love. The second one's much longer. Also very good are The Cat Who Walked Through Walls, which ties in to the same world as the other two, and I Shall Fear No Evil, along with, of course, Stranger in a Strange Land. Please, people. You can't not read this one. It's a classic! It's all but required!
Roger Zelazny
Wild, crazy, intricate fantasy. If you like really original imagery, strange new worlds, and a cast of convincing and consistent characters, you want to read his books. Sadly, he is no longer with us, so the second half of his Amber series shall remain forever unfinished.
Reccomended reading:
The Creatures of Light and Darknessis a very good stand-alone book of his, and Nine Princes in Amber is the first book in the Amber series, and an excellent intro to the wonderfully complex cosmology of the Amber books. He also has a collection of short stories and commentary called Unicorn Variations.
Claire Bateman
I only found out about her recently. She writes poetry the way I wish I
could. There's a dazzling quality to her work, along with some really
interesting viewpoints on science today.
Reccomended reading:
I haven't read anything of hers yet that I didn't like, but I especially reccomend the first book of poetry that I encountered, At the Funeral of the Ether. She has several other books out, including one called Friction which is quite good also.
Margaret Eleanor Atwood
She writes poetry. She writes short stories. She writes novels. She
does all of them well. Is there anything she can'tdo? She's
an incredibly personable writer. Her characters are real, unconventional,
convincing, and interesting. I read one of her novels recently and was
amazed, because I could completely empathize with allof her
three protagonist characters. They made sense, I liked them, they were
interesting, and they weren't carbon copies of each other.
Reccomended reading:
Thus far, I suggest The Robber Bride, which is one of her longer works, and The Handmaid's Tale, which is rather depressing, but still very good.
Stephen King
Hats off to the master! I may not care for all his work, but I will respect him forever for the Dark Tower series and his authorship of It. Please, everyone, don't just write the man off as a 'horror writer'. His talent goes far beyond that, and you'll be doing yourself and him a disservice by dismissing him so lightly.