Recommend me some books!...Please.

Anything by Robert A. Heinlein written before 1970, but especially:

The Moon Is a Harsh Mistress,
Have Spacesuit--Will Travel,
Double Star,
Citizen of the Galaxy,
Between Planets,
The Puppet Masters,
The Rolling Stones,
Starman Jones,
Time for the Stars,
The Star Beast,
Tunnel in the Sky, and
Sixth Column.

All the ones marked with asterisks were written as juvenile novels, and thus would be suitable for your niece (unless she's younger than 8 or 9). They might be considered a little mature by today's standards, but I think they're appropriate. The Rolling Stones doesn't have anything anyone would consider objectionable, and it's a cracking good yarn.

Have some more sci-fi books:

♦ Roger Zelazny -- The Lord of Light

♦ Clifford D. Simak -- City

♦ Olof Johannesson(Hannes Alfvén) -- The Great Computer: A Vision

♦ Lyuben Dilov -- The Weight of the Spacesuit

The Holy Quran. It will make your life much better if you decide to become a muslim.
no sarcasm here

Heroes Die by Matthew Stover and maybe The Devil You Know written by Mike Carey.
There's also The Witcher saga by Andrzej Sapkowski and great Metro 2033 by Dmitry Glukhovsky.

A series of unfortunate events.

"Good Omens" by Terry Pratchett & Neil Gaiman

Ender's Game quartet and Ender's Shadow series if you like the universe
1984
Brave New World
The Iliad (Might not fit your tastes but I liked it xD)

kid related other than Harry Potter I can't recommend anything

for you though A Song of Ice and Fire if you haven't read it is amazing and The Dresden Files is my favorite series ever.

Throwing in another recommendation for the A Song of Ice and Fire (Game of Thrones) series. Sooooo addicting! And thanks for the wishlist game! :)

The Mistborn series is very good! Actually pretty much anything by Brandon sanderson is worth a read. :D

I would recommend The Malazan Book of the Fallen series, starting with Gardens of the Moon. I would also recommend, Game of Thrones, The Way of Kings, Dune, Prince of Thorns, and Leviathan Wakes.

Here is also a great website I would recommend checking out: Goodreads

Odyssey.

A Song of Fire and Ice by George R.R. Martin (Game of Thrones as most people know it as), Ender's Game, and anything by H.G. Wells, and George Orwell.

I used to be a big fan of Clive Barker, loved Weaveworld and The Great and Secret Show. He also wrote a book intended for a younger audience, that was still a good read as an adult: The Thief of Always.

I don't know her age but I'd maybe suggest "Red Wolf Conspiracy" and it's sequels. It's actually good for all ages, I enjoyed it myself.

Others, Dresden Files, Temeraire novels, and the Kingkiller Chronicles. All are somewhat fantasyish (supernatural detective novels, historical fiction/fantasy, and fantasy, respectively)

I was supposed to write about Sci-fi/ fantasy books but I think that guys below have said enough already. I just couldn't miss the opportunity to share some books which can ignite the reading passion in an young individual :) . I can recommend for your niece Moomin saga by Tove Jansson, books by Astrid Lindgren - Pippi Longstocking series and other series , Selma Lagerlöf's The Wonderful Adventures of Nils , Jules Verne books (The Mysterious Island is a part of my childhood ! :) ). I would also recommend Treasure Island by Robert Louis Stevenson,Fairy Tales by Hans Christian Andersen and series by Karl Friedrich May (Winnetou etc.). A cherry on a top - In Desert and Wilderness by Henryk Sienkiewicz - a really nice story for a young reader. Books mentioned above are 100% suitable for a young reader - I've tested them on myself :) I wish you both all the best !

read don quixote of la mancha and the feast of the goat, you wont regret them

2 of the best books ive read recently are;
Ready Player One.
I lent this to 4 of my friends as soon as I had finished, and they all said it was amazing. I then re-read it as soon as I got it back!

Enders Game.
I had heard lots of good things about this book online, very easy to pickup and read. Almost as good as Ready Player One.

Ishmael an Adventure of the Mind and Spirit, Wizard: The Life and Times of Nikola Tesla : Biography of a Genius.

If noones suggested:

The power of 5 series
Maximum ride series
Eragon series

Try "Hatchet"
Its like an underrated version of the hunger games.Sorta....

The Horus Heresy series, 23 books in the series...so far :D

There are six pages in this thread so my apologies for not reading through them all before posting but...has anyone mentioned Chuck Palahniuk yet? Some might know him as "that guy who wrote Fight Club" but in my opinion, Fight Club isn't even his best work, although I suggest you read that as well even if you've seen the movie. I haven't read all of his books yet but I'm working on it. Invisible Monsters and Rant have been my favorites so far.

Another author I've gotten familiar over last couple of years is Harlan Coben. I'm not really a fan of detective stuff but I've enjoyed his Myron Bolitair series. Anything else, well...as a Finn I feel obliged to recommend Moomin books by Tove Jansson. They don't take too long to read and they are really profound books, more than you'd expect. They were written for adults after all, even though it's not uncommon in Finland to regard them as children's books. Appropriate for all ages. :)

Philip Pullman - His Dark Materials