This is copied form a thread on my guild's website. The ratings are based on an aggregate of guild member reviews.
Fantasy:
The Dark Tower Series by Stephen King
Dragonlance chronicles by Margaret Weis and Tracy Hickman
Death gate cycle series by Margaret Weis and Tracy Hickman
Iron Tower Trilogy by Dennis L. McKiernan
Wheel of Time Series by Robert Jordan
His Dark Materials trilogy by Philip Pullman
The Shanara series by Terry Brooks
the Mode series by Piers Anthony
Xanth series by Piers Anthony
Incarnations of Immortality series by Piers Anthony
Apprentice Adept seriest by Piers Anthony
Kushiel series by Jacqueline Carey
the Deverry series by katherine kerr
Chronicles of the Black Company by Glen Cook
Riftwar Saga by Raymond Feist
The Liveship Traders trilogy by Robin Hobb
A Song of Fire & Ice series by George R R Martin
Icewind Dale Trilogy by R. A. Salvatore
King Raven trilogy by Stephen R. Lawhead
Individual books
The Walking Drum by Louis L'Amour
Sinner by Ted Dekker
BLUE MOON RISING by Simon R. Green
Urban Fantasy:
Wicked years series by Gregory Maguire
Individual books
Wizard of 4th Street by Simon Hawke
Scifi:
Dune Series by Frank Herbert
Ender's series by Orson Scott Card
Individual books
1984 by George Orwell
Hmm...
I like Piers Anthony's Xanth Series though I haven't read much of his other work, but be warned if you can't stand often cheesy puns you'll be overloaded with them in this series.
I've kept up to date with Robert Jordan's Wheel of time and I'd recommend it highly, though I will admit it gets dry in sections there's a lot going on in those books. Since his death and the series being worked on heading for completion by Brandon Sanderson (who was chosen by Jordan's Widow), the writing style has changed a good bit, but the story is still gold.
Katherine Kerr, her books if you haven't read the Deverry Cycle can get quite confusing the story isn't exactly told chronologically, events in them happen over the course of several centuries, and as a present day event happens they'll often have a "Flashback" chapter to an event a hundred years earlier or more that set what just happened in motion. They are still excellent reading just the way it's laid out isn't always for everyone.
If any of us here have never picked up a book by Wies and Hickman, there's a problem. I'm not even going to start to explain the genius of their writing, but I will recommend the following books if you haven't read them.
The Soulforge, which delves into the young life of Rastlin and Caramon Majere starting at age 6 and concludes with his Test in the tower of High Sorcery.
Brothers in Arms, which picks up after Rastlin's testing, and follows his journey and first adventures as a War Wizard.
I'd also recommend The Prism Pentad by Troy Denning. If you played Dark Sun in the past, these will be familiar territory to you.
