Read Dracula and Jeckyl & Hyde.

Some great recommendations so far, special kudos to Breja's list. A few more:

Sci-fi: check out Peter F. Hamilton, Iain M. Banks, and C.J. Cherryh. Oh, and John Varley's Gaia Trilogy (if you can find it).
Fantasy: Robin Hobb's Farseer trilogy, Guy Gavriel Kay, and Patrick Rothfuss. Fritz Leiber is a must as well, IMO.

Others: Neal Stephenson, Dan Simmons

Just popping in to echo this recommendation! It's a great book.

For something lighter (but still quite meaningful!), I'd also recommend Terry Pratchett, as many others have here. Two I personally quite liked are Night Watch (although you might want to read "Guards! Guards!" first) and Thief of Time.

Can't go wrong with H.G Wells (especially The Invisible Man, Time Machine, and The Island of Dr Moreau), Jules Verne, and William Gibson.

One option is the A Song of Ice and Fire series. Even if you watched the show, there are still differences. Some of which the TV show did better and others the books did better.

If you like the Dragonlance books, there is a chance you will like the early books about Drizzt as well as a few other Forgotten Realms books.

Also, if you can understand old poetic writing, The Saga of the Volsungs might work for you.

On a side note, there are a couple of books based on Doom more specifically the first two games.

Some good ones, different genres, the first ones that come to my mind, avoiding the obvious classics:

Ian McEwan - Atonement
Agota Kristof - The Notebook/The Proof/The Third Lie (trilogy)
Haruki Murakami - Tokyo blues Norwegian wood
Stephen King - The Stand
Richard Matheson - I am legend
David Goodis - Shoot the piano player
Ray Bradbury - The martian chronicles
James Crumley - The last good kiss
Christopher Moore - A dirty job
Robert McLiam Wilson - Eureka Street

Malazan Book of the Fallen. Steven Erikson and Ian Cameron Esslemont have created a unique world with a lore spanning hundreds of thousands of years and seven continents. The writing gets better with each book. The storybis complex and complicated. Best fantasy fiction I've ever read.

maybe some Stephen King, I'm sure you'll find something to your liking.
gl!

Greg Egan is the "best" sci-fi writer. Tom Holt / KJ Parker is the "best" fantasy writer. Just pick anything and read it.

For mindfuck books (re: Fight Club), nothing cat beat Ubik (by Philip Dick, sci-fi) and An Ovel (by Raphael Slepon, fantasy). Both are serious adult books with little eckshun; if you're looking for the opposite, the absolute winner in both categories is Spectral Stalkers, a gamebook.

For tie-in novels (re: novels based on video games, except I've never seen a good novel based on a video game), there are two excellent trilogies: Chronicles of Athas 1, 2, 5 by Lynn Abbey (D&D, fantasy) and The Inquisition War by Ian Watson (40k, sci-fi).

These are some solid recommendations. Thanks guys!

Second this. Plus, if you end up like me, a tin foil hat wearing conspiracy theorist from ASOIAF, it gets even better. So many little things to blow your mind and let your imagination run wild with the possibilities.

For example, CLEGANEBOWL!!! GET HYPE!!!

Alternatively, you could read the Dunk and Egg novellas, they've been put together into a single compilation book not that long ago. It's more of a classic fantasy approach, of the knight errant, but set in the world of Ice and Fire, with all that it entails.

If you want something different I've heard Ice is good. It's apparently surreal and ambiguous so if you are into straight-forward writing or where you will think you understand everything at the end you might want to avoid it.

I also recommend the short story written by Nikolai Gogol, The Nose. Good to hear good things about it. It's on 6th place on my current to-read list.

I looked him up and apparently it seems he has written some books released in his real name and some with his pseudonym. Do you know why if that's true? A quick read of what he has written I like the look of Expecting Someone Taller. Have you read it?

If you like it, remember to also check out Lud-in-the-Mist. It's a 1926 novel by Hope Mirrlees. It was defiantely an influence on Jonathan Strange, shares the style and some themes. Neil Gaiman called it the most unjustifiably forgotten novel of the 20th century, and I'm inclined to agree. One of the very finest fantasy novels I've read. It should be considered a classic every bit as important as the works of Lord Dunsany and William Morris.

House of Leaves by Mark Z. Danielewski.
It's metafiction about a house that's bigger on the inside than the outside. I really can't describe it too much as part of the experience is reading it for the first time. Suffice to say, I rated it enough to take the trouble to buy a specific edition not available in the UK and get it sent here.

If you want pretty pictures to go along with your story, how about Hayao Miyazaki's Nausicaa of the Valley of Wind? Epic in every sense.

As a teenager, I really enjoyed Dealing with Dragons (Patricia Wrede). I love the way it playes with steriotypes and gender roles. (It starts by turning around the "Princess captured by Dragon" plot by having the princess deliberately run away to the dragon's lair.

If you want something that is just pure silliness (with a lot of puns and wordplay), you can check out The Phantom Toolbooth (I don't remember the author).