Forests Of The Night by S. Andrew Swann
It has been… but I don’t know if it counts. Some total hack (I forget who, but I remember the sick feeling in the pit of my stomach) was shopping around an adaptation of Flow My Tears… a ways back, and Paramount and Cruise/Wagner Productions optioned it – and then turned around and made Minority Report.
I don’t know if they were ever seriously considering making Flow My Tears…, though – the impression I had was that they may have been protecting themselves by sitting on a project that might have potentially devalued PKD as a box office draw.
Write your congressman! Err, I mean, Ridley Scott, or Terry Gilliam, or summat. 
Speaking of John Varley:
The Gaea Trilogy (Titan, Demon, Wizard) done in the same animation style of Fantastic Planet.
Steel Beach - would make a good mini-series.
Red Thunder - would be a good family movie with some minor tweaks
Olaf Stapledon.
Mutineer’s Moon by David Weber ( there has been on again/off again talk of an anime version )
Any number of the Bolo series of books/stories ( created by Keith Laumer; giant, sentient tanks ).
The Kundalini Equation would make a good martial arts/mysticsm movie.
Red Thunder would be good, I agree.
And his latest, “Mammoth”, has special appeal for me. Good visuals, too.
Iain M. Banks’ Use of Weapons. I envision it as a modern Blade Runner.
Harry Harrison’s Staineless Steel Rat series. Not the greatest SciFi by any reconning, but I’m sure would make a very entertaining set of movies if they got the right actor for the SSR.
Roger Zelazney’s Lord of Light.
SM Stirling’s Island in the Sea of Time trilogy.
That would be my pick. Charismatic anti-hero gentleman thief turned secret agent played by George Clooney, mad, bad and dangerous to know femme fatale played by Angelina Jolie, head of clandestine agency and retired legendary thief played by Sean Conney. A plot that practically is a screenplay already {Alan Grant wrote an excellent comic book adaptation of it years ago}, spaceships, exotic locations, and steam powered robots. Not great science-fiction, but hugely entertaining, and it would make the perfect movie.
Lots of good ideas, here.
My own list (apologies for some ancient references):
[ul]
[li]Lensman Series: would put Star Wars to shame[/li][li]Left Hand of Darkness[/li][li]Ringworld. The special effects alone would be great[/li][li]The Dispossessed (Le Guin)[/li][/ul]
Also, I have my own idea to sell: there’s this little kid, see, but he has amazing powers. At a young age, he’s invited to join this mystical society of warriors who protect the galaxy against evil. Unfortunately, he himself becomes evil, but then his son finds him and…
oh. never mind!
Well, how about this one, then. There’s this enormous spaceship from Earth, that flies from planet to planet doing scientific investigations. It has these really cool features, like a bar with windows that look out onto space, and a place where you can act out all your fantasies with holograms, and lots of really weird alien people walking around, and this one nerdy kid that everyone wants to beam into a bulkhead (see, “beaming” is when you disintegrate someone and send them somewhere by radio waves…).
No? Then how about…
Lots of great suggestions here.
I’d nominate some of John Barnes’ work. He’s doing some good hard contemporary sci fi, and is frequently compared (not unflatteringly) to Heinlein.
Orbital Resonance would kick some major ass on the big screen.
I find myself deeply conflicted about Kaleidescope Century because of the moral ambiguity of the narrator, but what a mindfuck flick that’d make.
And Mother of Storms would be sooooo much better than the recent climatological disaster dreck they’ve been serving up lately.
And, shifting briefly to Neal Stephenson, for the love of Og, would somebody please do Snowcrash before it gets too geriatric? Please? Or, The Big U, anyone?
For a more recent work, 1632 might be fun.
If you did it right, Hickam’s Back to the Moon might be an interesting miniseries. (“Doing it right” being the operative phrase. Actually, I think “total unholy nightmare to work with” would apply better.)
More horror than SF, but F. Paul Wilson’s Repairman Jack novels would make great movies.
Also in pre-production is The Moon is a Harsh Mistress, with screenplay by Tim Minear (Firefly, Wonderfalls, The Inside, X-Files, etc). I have big hopes for this one, as Minear ‘gets’ Heinlein in a big way.
I’ll second Left Hand of Darkness, althouth Left Hand of Dorkness would be a good substitute. 
Ender’s Game.
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Rendezvous with Rama.**
Foundation Triology (as a SciFi channel mini series)
I don’t know what you mean when you say that “a lot of the greatest stories have already been made into movies.” Not that many of the great science fiction stories have been made into films, and most of those that have were thoroughly messed up. I think it’s considerably more difficult to make a great story into a great film that you think.
Bippy the Beardless writes:
> Harry Harrison’s Staineless Steel Rat series. Not the greatest SciFi by any
> reconning, but I’m sure would make a very entertaining set of movies if they got
> the right actor for the SSR.
I just heard Harry Harrison talking about this subject in August. People have been trying to adapt The Stainless Steel Rat for decades. Many different producers have acquired options on the books and then hired writers to spend a while trying to turn it into an acceptable screenplay. Nobody has gotten it to the point where they’re willing to make the film. I don’t know why it’s so hard, but just recently I was talking to someone who’s worked as a writer, director, and producer for many years. He said that the problem is that, while it’s a great title and superficially an interesting story, it just wouldn’t work as a film. (I haven’t read the books, so I pass on offering my opinion on them.)
I meant “than you think”, not “that you think”. Incidentally, Harry Harrison is just fine with the fact that no one has made a The Stainless Steel Rat film. He loves the money he gets when he sells the options. He’s made much more money from not having The Stainless Steel Rat made into a film than he has from having Make Room, Make Room made into Soylent Green.
OH PLEASE GOD NOOOOOO
(as a SciFi channel mini series)
I think Miracle Mile may have been unofficially inspired by Niven’s story. They substituted a nuclear attack instead of a nova, but I believe it was a similar story about a man finding out the world was going to end and spending his last night with his girlfriend while trying to keep her from figuring out what was going to happen.
I’d love to see an Honor Harrington mini-series sort of like the Hornblower or Sharpe series. I think that would be SO cool if they did it right.
Also, I wouldn’t mind seeing something like John Ringo’s Hymn Before Battle series about the Poslene wars. It might be too bloody but I think a multi-part series a la Star Wars would be kick ass.
Michael Gears Forbidden Borders might also translate into a movie series fairly well I think.
Though not exactly SciFi I would LOVE to see a really well done mini-series about Stephen Kings Dark Tower.
-XT