In my opinion, here are some of the best Authors, Series, and Books for Young Adults.

Gail Carson Levine- Author of Ella Enchanted, Fairest. Her writing is mostly fantasy, written in a world filled with mystical creatures. Great for readers around the age of 9 to 13.

A Series of Unfortunate Events- A darker, but equally fasicnating series of three foster children, trying to escape the stories villian,Count Olaf. The ages recommended variey, depending on the maturity of the reader.( I have the first three books of this series avaliable.)

Fearless by Francine Pascal- A series by the well-known author of the Sweet Valley High books. Written in the late 90's, these books follow teenage girl Gaia Moore through her adventures in New York City. Recommended for teenagers.

White Oleander- Although not just a young adult book, the main character, Astrid, is a complex and likable character. Throughout the book, you follow her through foster care, and you feel as though you are growing with her. For Teens and Up.

Please write other Young Adult Books you enjoyed!

Hmmmm...I love this genre, so it's hard to choose, and I'm not sure what ages you're including in "young adult" so I'll just add a few and hope for the best!

The "Betsy-Tacy" series by Maud Hart Lovelace - my all time favorite series for children and young adults.  The series follows Betsy Ray, her family and friends through her childhood and early adulthood in turn of the century Minnesota.  The first four books in the series are definitely for children - I love to buy these for girls turning 7 or 8, and then the next four cover Betsy's high school years....no objectionable language or anything, but girls who are 12 to 13 and up will enjoy these.  The last two take place while Betsy is college age and cover her trip to Europe and her wedding.

The "Little House" series - must reads for all children and young adults.  If boys think they wouldn't be interested in these, just give them FARMER BOY as a stand alone.

The "Harry Potter" series - what else needs to be said about these.  The books get darker as Harry gets older, so they are a perfect series to age with the reader.

The "Tomorrow When the War Began" series - set in Australia, an unnamed foreign power invades the continent and a group of teens escape and are left to survive, then to help save their country.  For more mature readers (sex and violence are involved, the sex isn't graphic, but the violence might be disturbing to younger children).

I'm sure I'll think of others to add!

I really like YA an I read it a lot, so here's my list:

Guardians of Ga'Hoole series by Kathryn Lasky. 14 books so far and counting. This series is what I call 'Animal Fantasy', wthi talking animals as the main characters. The Ga'Hoole series is about owls.

Margaret Peterson Haddix. An amazing author. Her books are mostly future/suspense, I guess, but really, really good. She has a good series that's finished called the Shadow Children Sequence and a new series just started called The Missing, as well as several stand-alones.

The Ender series by Orson Scott Card. This series is among the best Science Fiction I have ever read. There is some language, but the stories are EXCELLENT!!

Cornelia Funke. She has written a couple stand alone books, but her best work IMO is the Inkheart Trilogy. It's a really great fantasy story. Book three is coming out later this year.

Pellinor Quartet by Alison Croggon. This is an epic fantasy about a girl with magic powers and a prophecy to fulfill. This is one of those series that stands out from the rest, an amazing and brilliant story.

The Inheritance Cycle by Christopher Paolini. This series is pretty much well-known, but I thought I'd mention it anyway. The writing isn't the best, or the story very original, but it's an enjoyable read nonetheless. Book three out of four is coming out in September.

Septimus Heap series by Angie Sage. Another seven-book young-wizard series. It starts out pretty mild in the first book, but books two and three increase in story and suspense quickly. Book four is coming out in less than a week, April 8.

The Lost Years of Merlin by T. A. Barron. This is a series about Merlin when he was a boy. I haven't read it in a few years, but as I recall it was quite good.

The Chanters of Tremaris trilogy by Kate Constable. Another amazing Australian author! This is another fantasy trilogy, where magic is done by singing, or 'Chantment'. It follows the adventures of Calwyn, who is unknowingly destined to become the famed 'Singer of All Songs'.

Artemis Fowl Series by Eoin Colfer. An interesting blend of magic, the present, and advanced technology. A good, and also funny, series. Book 6 is coming out later this year.

Uglies series by Scott Westerfeld. This is a series of four books, set in the future. They are very good.

The Book of Time by Guillaume Prevost. This is the first book in a seris about a boy who discovers a time-travel device in the basement of his father's book store. It's pretty good. Book two, Gate of Days, is coming out in October.

That's all I can think of at the moment.

-Rebekah

Don't forget the Dragon Trilogy (although on July 1st a fourth book is being published) by Chris D'Lacey.

My 8th grade students all read Lois Lowry's The Giver.  Then, several of them, also read the companion book Gathering Blue, and then the book that brings the first two together, The Messenger. 

Gloria Whelan - Listening for Lions, Once on This Island

Karen Hesse - Letters from Rifka, Out of the Dust, Rodzina

Jeanne Birdall - The Penderwicks

Richard Peck - A Long Way from Chicago, A Year Down Yonder

Madeline L'Engle - A Wrinkle in Time

Marcus Zusak - The Book Thief

Elizabeth Speare - The Sign of the Beaver

Carol Bierman - Journey to Ellis Island

Elise Carbone - Stealing Freedom

Seymour Reit - Behind Rebel Lines

How about the "Thursday Next Series" by Jasper Fforde; although they aren't quite finished yet, I've loved what's out there so far.

The City of Ember series by Jeanne Du Prau

I love the Gary Paulsen books that my kids read in 5th/6th grade.  Those were Hatchet, Dogsong, and The River.

At the older end of the scale - How about The Chronicles of Narnia series by CS Lewis?

And someone mentioned A Wrinkle in Time by Madeleine L'Engle, but I'd add the other 3 books of the Time Quartet.  They are (I'm testing my memory here) A Wind in the Door, A Swiftly Tilting Planet, and Many Waters.

Garth Nix  has several series that are fantasy related:

one is Keys to the Kingdom  book 6 is due in August.

He has an older series also that is being re-released here in the states:  The Seventh TOwer

My son has read them all and loves them..

I Ditto all the series listed above, Especially  The Shadow Children series by Margaret Peterson Haddix.  One of my "I hate to read" students was totally into this series.