Science Fiction
SF (or scifi, as coined by Forrest J. Ackerman) has been around for a very long time, though it's only in modern times (with H.G. Wells and Jules Verne) that the genre really began to solidify itself.

There are many definitions of science fiction; what I like is that it's a story where the science is integral, which is very broad, but SF itself is very broad. It has many sub-genres, such as cyberpunk, space opera, first contact, etc. A great list can be found here.

Modern SF owes much to Wells and Verne, and also to the pulps of the early twentieth century. Particularly with Amazing Stories (beginning in 1926 and helmed by Hugo Gernsback, after which the prestigious Hugo Awards are named) and Astounding Science Fiction, which were leaders of the field, showcasing talent upon talent, and taking the genre into unknown, deep, and highly imaginative territory. Astounding (nowadays Analog SF) was helmed by a great editor (and also author), John W. Campbell.

The 20's and 30's were a boon for the genre. Authors such as E.E. "Doc" Smith, Cliff Simak, A.E. van Vogt, Jack Williamson, and Theodore Sturgeon were to inspire many of the coming generation that would comprise, "The Golden Age".

Of the the Golden Age writers, three stand out as the big three: Isaac Asimov, Arthur C. Clarke, and Robert Heinlein. All were exceptional writers, creative thinkers, and helped expand the genre.
After the Golden Age, an era of New Wave began (circa the 60's). Writers of this era include Robert Silverberg, Harlan Ellison, and Philip Jose Farmer, all of whom are still writing and publishing today.

The 1980's saw the beginning of a popular sub-genre: cyberpunk (particularly with the award winning Neuromancer by William Gibson.

Todays SF is very broad, from Star Wars novels to Jack Williamson (who is still writing at over ninety years of age), and even the pulps, Asimov's Science Fiction, F&SF, and Analog. It's a wonderful genre, and continues to enthrall young and old alike.

Wikipedia Links of Interest
Science Fiction
History of SF
Golden Age of SF
Hard SF
Soft SF
SF Fandom
SF Conventions
List of SF Authors
List of SF Awards
List of SF Novels
Asimov's Three Laws of Robotics
Clarke's Three Laws

For more links, go to this site's links section.

Recommended Reading

Foundation by Isaac Asimov
Foundation and Empire by Isaac Asimov
Second Foundation by Isaac Asimov
The Caves of Steel by Isaac Asimov
I, Robot by Isaac Asimov
Blood Music by Greg Bear
In the Ocean of Night by Gregory Benford
Across the Sea of Suns by Gregory Benford
Great Sky River by Gregory Benford
Tides of Light by Gregory Benford
Furious Gulf by Gregory Benford
Sailing Bright Eternity by Gregory Benford
The Demolished Man by Alfred Bester
The Stars My Destination by Alfred Bester
The Martian Chronicles by Ray Bradbury
Bloodchild and Other Stories by Octavia E. Butler
Dawn by Octavia E. Butler
Adulthood Rites by Octavia E. Butler<
Imago by Octavia E. Butler
Parable of the Sower by Octavia E. Butler
Ender's Game by Orson Scott Card
Ender's Shadow by Orson Scott Card
Rendezvous with Rama by Arthur C. Clarke
Do Androids Dream of Electric Sheep? by Philip K. Dick
Dangerous Visions edited by Harlan Ellison
To Your Scattered Bodies Go by Phillip Jose Farmer
The Fabulous Riverboat by Phillip Jose Farmer
The Dark Design by Phillip Jose Farmer
The Magic Labyrinth by Phillip Jose Farmer
Neuromancer by William Gibson
Stranger in a Strange Land by Robert Heinlein
Dune by Frank Herbert
Children of Dune by Frank Herbert
The Moon and the Sun by Vonda McIntyre
Paradox by John Meaney
Context by John Meaney
Resolution by John Meaney
CUSP by Robert A. Metzger
A Canticle for Leibowitz by Walter M. Miller, Jr.
Marrow by Robert Reed
Kirinyaga by Mike Resnick
Revelation Space by Alastair Reynolds
Red Mars by Kim Stanley Robinson
Blue Mars by Kim Stanley Robinson
Green Mars by Kim Stanley Robinson
Old Man's War by John Scalzi
Frankenstein by Mary Shelley
Lord Valentine's Castle by Robert Silverberg
City by Cliff Simak
The Last and the First Men by Olaf Stapleton
More Than Human by Theodore Sturgeon
20,000 Leagues Under the Sea by Jules Verne
Slaughterhouse Five by Kurt Vonnegut
The Time Machine by H.G. Wells
War of the Worlds by H.G. Wells
Neverness by David Zindell
The Broken God by David Zindell
The Wild by David Zindell