The House of Leaves - Mark Z. Danielewski

It will leave you feeling disturbed.

I second The Day of the Triffids and Kurt Vonnegut. Especially Vonnegut's "Cat's Cradle" and "Player Piano" (should be in a short story collection).

Also if you like 1984, you may also read "We" by Zamyatin and "Brave New World" by Huxley to complete the dystopian trilogy cylcle.

Seconding His Dark Materials here. Friggin' amazing.

Also, most anything by Brian Cornwell. Sure, there are a couple of his books which are not that great, but Stonehenge was an absolute masterpiece.
Hitchiker's also one of my favourites, though only the first three books, I think he went a bit overboard with the last two.

Oh, and if you're into poetry and know a bit of archaic Portuguese, Os Lusiadas is just about the most godawesome brainblasting book ever. Plus, I heard it's even free to download.

I'm currently really into alternate history, so if you like that kind of thing, I'd recommend Harry Turtledove, some really good "what ifs". He also writes pretty decent fantasy. Oh, and Michael Crichton. I'm surprised no one has mentioned him yet.

Neal Stephenson has some excellent books (particularly Cryptonomicon), though they're also the longest novels I've ever really read at over 1000 pages.

Asimov is excellent. Start with Foundation.

The Night Angel trilogy by Brent weeks is the best book series I've ever read, bar none.

Neil Gaiman is also pretty excellent, with his best probably being American Gods.

The Dresden Files is excellent for lighter reading.

Georger Orwell's Animal Farm.

Pretty good book, I enjoyed it a lot.

Just gonna throw Bernard Cornwell in

Metro 2033 was an awesome book, barring some translation errors, and the atmosphere really dragged me in.
It also had some cool stuff about the power of thought.

There is a book series out there with the title 'Circle of Three', I read the first in the series and did find it hard to put down, but I can't say I could relate to any of the sequels. Worth a go though.
Or you could go really retro/old-school and read Goosebumps... lol

A Song of Ice and Fire
A Fire Upon the Deep
A Deepness in the Sky
Pushing Ice
Chasm City

Hehe, read only. If you want something gimme a PM

Les Misérables

It's one of the best books I've ever read. It's very, very good.

Roadside Picnic
Wolves Eat Dogs
Anthem
Animal Farm
The Improvised Munitions Handbook

metro 2034-atmosphere...oooohh the atmosphere.
World war Z-really interesting to read, love the style.
The zombie survival guide-basically just a joke on survival guides, but it's good reading.
The Road-great atmosphere, story and character relationships.
Discworld-ALL OF THEM. go here to see in wich order to read them
Good Omens-by the guy who wrote discworld, amazing stuff.
The chronicles of Narnia-again, read all the books, good stuff, if you like fantasy.
The Good Soldier Švejk- or schveik, or schvejk. satire at it's greatest. read only the first two books. the author died before he could finish the last one.
The Lamb-incredibly good comedy, very good jesus-related jokes (actually his friend)
also, books by Arto Paasilinna. good stuff, if you like scandinavian black humour.

as you can see, i have listed quite a few comedical works. enjoy!

Art of War. a book that never leaves you disappointing