Anything by tamora pierce :D, chronicles of ancient darkness, black magician trilogy, riftwar saga, twilight.

• The Twilight Series by Stephenie Meyer
• The Inheritence Series by Christopher Paloini
• The Harry Potter Series by J.K. Rowling
• The Shadow Children Series by Margaret Peterson Haddix
• The Lord of the Rings Series by J.R.R. Tolkien
• The Warriors Series by Erin Hunter
• The Hunger games trilogy by Suzanne Collins
• I am number 4 book by Pittacus Lore
• Chronicles of Narnia by C. S. Lewis
• The Maximum Ride Series by James Patterson
• The Frog Princess Series (for girls) by E. D. Baker
• The Daniel X Series by James Patterson

I love these books and I hope you will too! =)

The Abhorsen Trilogy by Garth Nix

The Seventh Tower Series by Garth Nix

The Keys to the Kingdom by Garth Nix

Any StarWars novels

Something wicked this way comes by Ray Bradbury

Anything by Asimov is good, but some are probably a bit esoteric for a beginning reader. Heinlein is probably the classic. Starship Troopers was supposedly required reading at the Naval Academy at one point. I would point them at some anthologies, the ones that Asimov edited where really good, providing history and background to go with the stories.

Don't forget Jack Chalker. Chalker writes on a level easily deciphered by young adults, and offers pure escapism in his novels.

If not Heinlein or Asimov, everyone should read Ray Bradbury. Bradbury is on of the foundational writers of science fiction. The world's loss of Mr. Bradbury in 2012 was a tragedy. His legacy will live forever though. His novels and short stories span every level of reading ability, and no one will ever waste time reading anything he crafted. Look for Dandelion Wine, Something Wicked This Way Comes, The Illustrated Man, The October Country, The Martian Chronicles, R is for Rocket, I Sing the Body Electric, and hundreds of other titles.

Don't forget Harlan Ellison or H.P. Lovecraft, but be wary that many of their stories can be either disturbing or contain higher level content.

Arthur C. Clarke is another hugely important science fiction writer. Mr. Clarke's knowledge was critical to the development of the NASA programs and he consulted for decade on the space programs of many nations. One of Clarke's greatest legacies was the novel Childhood's End. A bit dark, it deals with issues of first contact, paranoia, utopia/dystopia, and the transformation of the entire human race.

• Madelyne L'Engle - wrote the Time series (A Wrinkle in Time, A Wind in the Door, A Swiftly Tilting Planet, Many Waters) and other tales of ordinary teenagers facing extraordinary circumstances
• Robert Anson Heinlein - an old school writer who wrote a lot of Young Adult scifi, particularly "boys' stories" - best known for The Rolling Stones and Starship Troopers
• Andre Norton - another old school writer, Andre was actually a woman writer in an age where "only" men wrote scifi - wrote many books about teens coming of age in strange worlds, and learning to survive in strange situations - books include Beastmaster (which is nothing like the movie) and Star Man's Son
• Margaret Peterson Haddix - wrote the Shadow Series - a futuristic world where population is strictly controlled and "shadow children" who are illegal "extra" kids try to survive and grow up, along with other books
• Virginia Hamilton - wrote Justice and her Brothers - the first scifi series about an African-American teen
• Orson Scott Card - best known for his Ender's science fiction series (Ender's Game, Ender's Shadow, etc)
• Anne MacCaffrey (lately helped by son Todd) - wrote the Dragonriders of Pern series - people on another world cope with danger by bioengeneering "dragons" from native animals. Ms. McCaffrey also wrote the Crystal Singer novels with which many young women can easily associate.
• Larry Niven - Probably best known for his Known Universe series and the Ringworld novels.
• Scott Westerfield - wrote the Uglies series (Uglies, Pretties, Specials, Extras) about a futuristic society where people are expected to be beautiful

• Terry Pratchett - best known for the Discworld series, he also does a great series about a teenage witch coming of age (The Wee Free Men, A Hat Full of Sky, Wintersmith) - the Discworld series is comedy
• Tamora Pierce - writes stories of teens (especially girls) coming of age in a medieval-type world
• Brian Jacques - best known for the Redwall series, about anthropormorphic animals who build and defend Redwall Abbey - either younger kids or teens can enjoy these books
• Jane Yolen - writes fantasy books like Owl Moon
• Patricia C. Wrede - writes humorous fantasy about teens (usually girls)
• JK Rowling - wrote the Harry Potter books
• Diana Wynne Jones - wrote humorous fantasy like Howl's Moving Castle and Dogsbody - often involves teens learning to use their powers
• CS Lewis - best known for the Narnia series, which is currently being made into popular movies - deals with children who are sent to a magical world to solve problems
• Susan Cooper - best known for the Dark is Rising series - about children and teens who have to cope with mystical forces of good and evil
• TA Barron - writes about Merlin and his descendants living in a mystical world
• Victoria Hanley - wrote The Seer and the Swordand The Healer's Keep
• Garth Nix - best known for the Abhorsen Series (Sabriel, Lirael, Abhorsen) and the Seventh Tower series - deals with teens coming into power
• Eoin Colfer - writes the Artemis Fowl series - about a young mastermind who schemes to make money by using the faerie and elven worlds
• Katharine Eliska Kimbriel - her books are usually out of print, but worth finding, especially Night Calls and Kindred Rites, the stories of a young witch learning to use her powers.
• Phillip Pullman - wrote the His Dark Materials trilogy (The Golden Compass, The Subtle Knife, The Amber Spyglass) - deals with coming of age in a world where a person's soul exists outside of their body
• Alan Garner - The Owl Service, Elidor, Red Shift et al.
• Frank Herbet, et al. - The Dune series originated with Frank, but was carried on by his son after Frank's death. Wonderful fiction, all of it.
• David Drake - Drake took military writing and placed it firmly within SciFi with Hammer's Slammers.
• Joe Haldeman - One of the single best SciFi military works was written by Haldeman. Look for The Forever War.

• Dancing With an Alien by Mary Logue
• The Dark Side of Nowhere and Downsiders by Neal Shusterman
• Spacer and Rat by Margaret Bechard
• Tria and the Great Star Rescue by Rebecca Kraft Rector
• Mr. Was by Pete Hautman
• Phoenix Rising by Karen Hesse
• Dawn Palace and Winds of Mars by H.M. Hoover
• Goose Chase by Patrice Kindl
• Mrs. Frisby and the Rats of NIMH by Robert C. O'Brien
• Eragon and Eldest by Christopher Paolini
• The Earthsea books by Ursula Le Guin
• The Twilight Saga by Stephanie Meyers

I would like to add Alan Dean Foster to this list. As a teen, I read many of his novels and each time was swept away into the story. Mr. Foster has a unique way of telling a story that just draws you into the worlds he creates with vivid detail. My favorites were the Star Trek Log Books, and one of the first non-Lucas Star Wars novels, Splinter of the Minds Eye. Consider reading one of his best novels, Nor Crystal Tears.

But my favorite one of all are the Flinx and Pip novels.

• For Love of Mother-Not (1983)
• The Tar-Aiym Krang (1972)
• Orphan Star (1977)
• The End of the Matter (1977)
• Flinx in Flux (1988)
• Mid-Flinx (1995)
• Reunion (2001)
• Flinx's Folly (2003)
• Sliding Scales (2004)
• Running from the Deity (2005)
• Bloodhype (1973)
• Trouble Magnet (2006)
• Patrimony (2007)
• Flinx Transcendent (2008)
• Impossible Places (2009)

I've read all these several times, and they still are thrilling to read.

I highly recommend them!

The beauty of the science fiction genre, that has not been touched on here, is that every other genre can neatly fit within it. Every story can be told from a SciFi perspective, be it western, romance, mystery, thriller, or any other type of writing.

Here's a hint for finding good science fiction and fantasy:

While most of the cover art of these two genres get panned often as cheesy or baudy, some of the best novels are covered by the same artists. Look for stories you like to read, then check on the copyright page for the artist who drew the cover. Chances are you will see names like Michael Whelan, Rowena (Morrill), Donna Diamond, and H.R. Van Dongen (a classic pulp cover artist), as well as many others. Look for these artists and the story under the cover is likely to be a good one.