Recommend me some books!...Please.

I'm echoing a few suggestions here, but I think you'll enjoy a couple of my favourites. I highly recommend Ender's Game, and pretty much all the books in the Enderverse. Ender's Game is one of my favourite books of all time, the writing really clicked with me. Speaking of my favourite books, His Dark Materials is something I read a couple of times each year. There was a film based off the first book, it was called The Golden Compass. It had reasonably good casting, apart from the main character which they got completely wrong in my eyes. The film didn't come close to doing this epic tale justice though.

Thanks for coming up with the thread, I've got some ideas for my reading list from here! ;)

Hehe, I just had a stupid, yet mildly amusing thought. I enjoy various books based on Video Game universes...Someone needs to make a Minecraft Book! Hehehee.....I'd honestly read it and probably love it if it was written well enough.

Here's a fun read, "98.6, The Art of Keeping Your Ass Alive"
Take with you when you go camping. :D

I would highly recommend the Temeraire series by Naomi Novik, they are excellent reads.

1984

Although you probably already know him, my favourite Scifi author is Stanislaw Lem.
You can't really go wrong with any of his books but from his more serious scifi novels I especially recommend "Fiasco". It's about an human expedition to a distant world to achieve the first contact with a different intelligent species.
The novel touches many interesting technical and philosophical topics (problems of finding and getting to a civilization evolved enough to communicate to, AIs, cryogenics, limits of human understanding and problems in dealing with things beyond it,...).

If you enjoy some humour with your scifi, go for his "Star Diaries". It's a collection of stories about the fantastical (in every sense) adventures of the kosmonaut Ijon Tichy. It has many funny parts but it does deal some philosophical questions and interesting intellectuals games as well. On the back of my edition Ijon Tichy is called a "cosmic Münchhausen" which is a fitting description IMO.

Last but not least his non-scifi books are excellent, too. In fact one of them is my absolute favourite among his works: "A Perfect Vacuum". It is a collection of fictional reviews of fictional books (well almost only fictional books, one of the reviews is about a book called A Perfect Vacuum which contains several fictional reviews of fictional books). The book is full of ideas for unwrittable books, philosophical mindgames and humour.

As for niece: One of the first real books I read was the first from the "Caius" series by Henry Winterfeld. Essentially the books are about the adventures of Caius, some kind of kid-detective, in ancient Rome. The books are great and pretty much suitable for any age. Unfortunately I'm not sure if the books are also available in English.
EDIT: After a bit of googling it turns out two of three books from the series were translated into English and published as Detectives in togas and Mystery of the Roman ransom

Dresden Files is IMO a good series. Zombie survival guide and world war z. Girl with Dragon tattoo series. The stuff of thought. the truth about honesty.

I'll try not to repeat titles that I've already seen in this thread.

[Fantasy]

• The Xanth saga by Piers Anthony (Book #1: A Spell for Chameleon) - light fantasy with puns; I'd stop after about book 12, as by that point he's trying to incorporate every pun that readers sent in to him rather than writing good stories. IIRC, book #5 of the saga (Ogre, Ogre) is notable for being the first fantasy novel to reach the New York Times bestsellers list.
• The Temeraire saga by Naomi Novik (Book #1: His Majesty's Dragon) - Historical Fiction - what if dragons really existed during the Napoleonic Wars
• The Halfblood Chronicles by Andre Norton & Mercedes Lackey (Book #1: The Elvenbane) - Elves rule over humans as harsh slave drivers, but there is a prophesy that a half-blood will be born who will lead the humans to freedom.

[Urban Fantasy]

• The Incarnations of Immortality saga by Piers Anthony (Book #1: On a Pale Horse) - the series follows the office holders of the positions of Death, Time, Fate, War, Nature, Evil, & Good.
• The Apprentice Adept saga by Piers Anthony (Book #1: Split Infinity) - Two worlds, one scientific, one magical are linked. A man on the scientific world survives an attempt on his life when he accidentally discovers a passage to a magical world that is a direct analog to his homeworld.

[Science Fiction]

• The Lost Fleet Saga by Jack Campbell (Book #1: Dauntless) - Military SciFi - the Legendary Hero has returned as prophesied to end a century-long war; he's just a man, but he remembers techniques of warfare that have been forgotten.
• The Retrieval Artist saga by Kristine Katheryn Rusch (Book #1: The Disappeared) - Cultural Conflict between humanity and several alien races now present in the Solar system; CSI on the moon.
• The Sprawl saga by William Gibson (Book #1: Neuromancer) - although Philip K. Dick was writing similar material 20 year earlier (such as the previously mentioned 'Do Androids Dream of Electric Sheep' [Blade Runner], 'We Can Remember it for You Wholesale' [Total Recall], "Second Variety' [Screamers], 'Minority Report', and 'Paycheck'), Gibson is cited as the father of modern Cyberpunk. This is his defining trilogy. A number of related short stories that are considered prequels (with some unrelated) can also be found in the anthology 'Burning Chrome'. The most notable of the prequel tales are Johnny Mnemonic, and Burning Chrome.

I've also got a few more recommendations I can post if you're willing to try historical fiction.

I enjoyed the Wheel of Time series by Robert Jordan, they are long books but good ones.

I second everyone suggesting Malazan Book of the Fallen - awesome, but quite demanding books. You're thrown right into the middle of not only events happening during the books, but also in the middle of history of world quite different from regular fantasy books - so you either drown, or learn to swim in it.
And as for you niece - what about The Graveyard book or Coraline from Neil Gaiman?

I don't know if you're into Halo at all, but I thought the first 3 Halo books were pretty good. =P I haven't read any of the others yet.

lotsa book to think of and already posted, let me just give a shout out to a book I'm currently reading: Hyperversum by Cecilia Randall. Some folks are playing virtual reality RPG and bam, suddenly end up back in time in medieval times. It's mostly about a group of present day folks that get ported to rather grim and brutal times so helllo you actually have to earn your food, likely kill other people, and generally your life doesn't mean all that much. Not a game anymore xD Maybe an eye opener to people who'd actually want to live in some game worlds and forget it's not a fairy tale. Nice reading so far tho I didn't read all that much yet.

EDIT: oh I see some problem I guess, seems it's only Italian (original) or Polish :D

House of Leaves

If you want a fast, fun, action-packed science-fantasy-styled read that's still vastly better written than anything on the market, check out "Lord of Light" by Roger Zelazny.
If you want a deep, sophisticated journey into the human condition via an incredibly well written science-fantasy novel, check out the Sword/Claw/whatever of the Executioner/Citadel/whatever quadrology by Gene Wolfe. His talent with words is mind-blowing, and it's the closest fantasy novels have come to true literature since Tolkien. (Adults only.)

Unfinished Tales and The Silmarillion by Tolkien were good reads if you get into the LotR series. Still good even if you don't though.

And for Sci-Fi I really enjoyed the Republic Commando Series

Anything by David foster Wallace, but I would start with "the broom of the system."

Also, books I enjoyed recently would be "trainspotting ," and "naked lunch"

Hunger Games triology by Suzanne Collins, Harry Potter books by J.K.Rowling, Da Vinci Code by Dan Brawn or his other books, Sword of Truth by Terry Gookind, I personally don't read books, I hear all them if can express like that XD, I mean instead of read I hear audiobooks.

Your niece would absolutely love The Naked Lunch by William S. Burroughs or The politics of Ecstasy by Timothy Leary.

If you are really looking for something to keep your interest try the wheel of time. It will keep you occupied for a good long while.

Black Library series : Horus Heresy
J.R.R.Tolkien
Fundation by Asimov
R.R. Martins Song of Ice and Fire Herberts Diune series
Kings Bastion Glukhovskys Metro 2033

Brent Week's Lightbringer and Night Angel series, and Sam Bowring's Broken Well and Strange Threads series are all excellent fantasy series.

G.R.R Martin's 'A Song of Ice and Fire' is also amazing, & Kevin J Anderson's Saga of Seven Suns.

A book that's great for young readers? I would suggest reading these yourself to see if you think it's appropriate, but I strongly suggest Starlight Crystal (Christopher Pike). It's a great story that folds in on itself and challenges one's perspective of belief, morality & religion. I loved it as a kid and had to get it so I could read it again.

If she hasn't read any of Rick Riordan's collections, I'd strongly suggest getting those. I've read all of his Percy Jackson & Heroes of Olympus series, but haven't managed to pick up his Chronicles of Kane series or any of his other novels. There's also the Ranger's Apprentice that I've been meaning to pick up, though I'm not sure how good it is.

I also have bits and pieces of the Artemis Fowl collection, but I haven't read it yet.

As for some more of the fantasy series (and I don't recall this being too inappropriate, but I haven't read it in a while), you might want to look into reading some Stephen Lawhead. I read his Songs of Albion series and loved it. I'm on the third installment of his King Raven trilogy (based off Robin Hood). His other series that I want to get are "Dragon King Trilogy" "The Pendragon Cycle" and "The Celtic Crusades".

I read a lot of hard science fiction, so I have the most experience there.
Some authors and books:

SF:
Vernor Vinge: Across Realtime series, Zones of Thought series, Rainbows End (note lack of possessive).
David Brin: Uplift series, Earth, The Postman, Existence (currently reading, it's an incredibly realistic near-future novel that deals with SETI, technophobia, the long term future of the human race, and how we balance the needs of humans with those of animals or even aliens, all in an engaging, hypothetical manner)
Neuromancer, by William Gibson: classic (the original) cyberpunk. Mature.
2001: A space Odyssey, by Arthur C. Clarke: Read it now. It's short.
Authors I wholeheartedly recommend, in no particular order: Vernor Vinge, David Brin, Arthur C. Clarke, Isaac Asimov, Greg Egan (caution: hardcore science--he has derivations of formulas in the text), Dan Simmons, George Orwell, Stephen Baxter, and more that I can't think of off the top of my head.

Fantasy:
An excellent fantasy book: A Wizard of Earthsea (Earthsea Cycle #1) by Ursula K. Le Guin. I think it's young adult, but I read it when I was younger than that, and think it's still engaging for an adult audience. (Miyazaki film was based on it)
Young adult-ish fantasy: Inkheart + rest of series by Cornelia Funke.
Classic children's (although a lot of it went over my head when I first read it) fantasy/sf: A Wrinkle in Time by Madeleine L'Engle
Children's fantasy book: Howl's Moving Castle, by Diana Wynne Jones (Miyazaki film was based on it. Huh, I read a lot of the books he adapted into movies before he adapted them, apparently)
I will second everything by Terry Pratchett.

Nonfiction:
Freakonomics: A Rogue Economist Explores the Hidden Side of Everything: so much fascinating information about all topics
Just My Type: A Book About Fonts by Simon Garfield: Fascinating to me.
Surely You're Joking, Mr. Feynman: Memoir-ish about a Nobel in physics laureate, and really funny

The Sword of Truth series by Terry Goodkind. http://www.sword-of-truth.com/books/the-sword-of-truth

The outsiders.