My top...errr...9. And my picks from their works.

Frank Herbert (Dune)
Robert Heinlein (Stranger in a Strange Land)
Arthur Clarke (2001)
Isaac Asimov (Foundation)
Douglas Adams (The Hitchhiker's Guide to the Galaxy)
Jules Verne (20,000 Leagues Under the Sea)
H.G. Wells (The Time Machine)
Orson Scott Card (Ender's Game)
Kim Stanley Robinson (Red Mars)

carl sagan

We always said ff was a man of few words......ah wait, that was just me...nevermind

star wars

i only have one word to say:

Rodenberry(however the heck you spell it) > everyone else

That's 9 words. And that's an affront to the masters of Science-Fiction. We will take your water for the good of the tribe and grok its fullness while we contemplate how to eliminate your legacy (see if you can catch those references).

i like fred's list with two minor alterations:
Robert.Heinlein
Issac Asimov
Gordon Dickson
Lois McMaster- Bujold
->terry pratchet
Arthur C.Clarke
->alan dean foster
Harry Harrison
Jack Chalker
Keith Laumer

in order
mccaffrey
asimov
moon
scarborough
leonardo davinci
(various ancient indian (asia) writers ) google Vimanas
there are many oters of note but these are what id limit my selections to
are they all scifi well all have been considered thus

I shall attempt to grok it's fullness at a later time...I am only an egg.

no one's mentioned Larry Niven yet. I presume most of you like Halo? it was lifted directly from Ringworld.

Orson Scott Card. Simple.

Digital Anvil
Joss Whedon (Firefly, anyone?)

For me sci-fi was gaming and movies when growing up. Literature sci-fi would have been perhaps a bit darker and much more grounded though still, imo, sci-fi in as much as they are based on future worlds, societies and technologies which devloped from our own. 1984, A Clockwork Orange and A Brave New World come to mind.

Beyond Arthur C Clarke I never really clicked with outright robots and space ships type of stuff on paper. Perhaps my opinion is tainted by the memories of having read Philoi K Dick. Great ideas poorly written well filmed

Larry Niven Taw. Absotively posilutely.

(To think that Heinlein published Starship Troopers in 1960!)

Hey! What about Poul Anderson? And does no one like
Ursula Le Guin? I also like Philip Jose Farmer ... or is he not
sciency enough?