Stephenson, Brin, Bear, Wilson, Gibson. Nancy Kress and Connie Willis write harder science than many women.
Yet another recommendation for Neal Stephenson.
I’d like to add an author that hasn’t been mentioned yet. Jonathem Lethem has written some insanely excellent stuff. I’d start with Gun, With Occasional Music, then move on over to Amnesia Moon and As She Climbed Across the Table. His short story collection The Wall of the Sky, The Wall of the Eye is worth reading, and his non-science fiction novel Motherless Brooklyn is a keeper.
Go find a copy of Zodiac by Stephenson too. It’s set in Boston and deals with chemical dumping…written with the same sarcastic humor as Cryptopnomicon.
I sill haven’t read The Big U by Stephenson(in fact I’ve only seen the book once), but I would rank his books :
Cryptonomicon (probably my favorite book ever)
Diamond Age
Snow Crash
Zodiac
in the new release of Crypto. in small paperback form, there is an excerpt from his new book.
Poul Anderson: The Dancer from Atlantis, Brain Wave, Tau Zero, A Knight of Ghosts and Shadows, The Rebel Worlds, Flandry of Terra, People of the Wind, The Earth Book of Stormgate, Fire Time.
Fritz Leiber: The Silver Eggheads, Gather, Darkness! The Best of Fritz Leiber (a collection of short stories, but some of them are fantasy)
Eric Frank Russell: Sinister Barrier, Sentinels of Space, Wasp, Three to Conquer (this guy is the most underrated sci-fi writer, and I don’t understand why) [P.S. Jack Chalker likes his stuff. Good luck on finding it.]
Ray Bradbury: The Illustrated Man, S is for Space, The Martian Chronicles
Fredric Brown: Martians, Go Home! Not only is this a screamingly hilarious novel, it is a classic example of John W. Campbell, Jr.'s dictum of take a situation and examine all possible implications.
Leigh Brackett: The Long Tomorrow, the Skaith trilogy, The Best of Leigh Brackett – hell, I’d read anything by Brackett. She was the scriptwriter on the only Star Wars movie that was worth a steaming pile of shit (The Empire Strikes Back)
Andre Norton’s Solar Queen tetralogy: Sargasso of Space, Plague Ship, Voodoo Planet, and Postmarked the Stars.
I second Ellison on short story collections. I recommend Deathbird Stories and Strange Wine. I also suggest his anthology Dangerous Visions; it’s seminal in the field. I also second Dick; check out his novel “The Man in the High Castle.”
Since you said you like novellas, by all means check out The Science Fiction Hall of Fame Volumes 2A and 2B; I don’t think you’ll be sorry. (Volume 1 focuses on short stories, but it’s damn good, too.)
I highly recommend James Triptee, Jr.'s novella “The Only Neat Thing to Do.” And though he’s generally considered a horror writer, I would check out H.P. Lovecraft’s novellas “At the Mountains of Madness,” “The Shadow out of Time,” “Dreams in the Witch-House,” and “The Whisperer in Darkness.”
Jack Vance: To Live Forever, The Many Worlds of Magnus Ridolph
C. M. Kornbluth: The Space Merchants (with Fred Pohl) and The Syndic and Not This August (solo)