My information comes from the list at Teens Read Too; blurbs are from Amazon unless otherwise mentioned.
For 9-12 year olds:
Any Which Wall, by Laurel Snyder. Here's what I said in my review: "Henry and his little sister Emma, Henry's best friend Roy and his big sister Susan (who has to "look after" the others) are not particularly looking forward to a long, hot, Iowa summer. Then they find the Wall, a wall in the middle of a cornfield, a wall that isn't walling anything...a wall that is magic, and will take them to any other wall that ever might have been. Wizards, pirates, outlaws, a lovable, and enormous dog who needs a home, and more, await them, in a splendiferously fun journey through time and space in the best Edward Eager tradition of great characterization, brisk writing, and snappy dialogue among the children."
The Deep, by Helen Dunmore. "Sapphire lives in two worlds. On land she walks the rocky shores of the Cornwall coast—but under the sea she can swim like a seal by the side of her Mer friend Faro. Now both of Sapphy's worlds are threatened. In the profound depths of the ocean, where the Mer cannot go, a monster called the Kraken is stirring. He has the power to sweep Ingo away and shake the land from its foundation."
The Dragon Diary: Dragonology Chronicles Volume 2 (Ologies), by Dugald A. Steer. "Fresh from recovering the Dragon’s Eye, apprentice dragonologists Daniel and Beatrice Cook eagerly await the hatching of the dragon’s egg in their care. But just as the shell begins to crack, their mentor, Dr. Ernest Drake, is called off to India to look for their missing parents and tend to the gravely ill naga dragons they’ve left behind. Meanwhile, the siblings receive a tip that the secret to curing dragons may lie in an age-old Dragon Diary, if only they could decipher it!"
Oracles of Delphi Keep, by Victoria Laurie. "Along the southern coast of England, atop the White Cliffs of Dover, stands a castle. And at that castle’s old keep is an orphanage. Delphi Keep has seen many youngsters come and go through its gates, and Ian Wigby and his sister, Theodosia, are happy to call it home. Life has always been simple at the Keep, and the orphanage safe, until one day, Ian and Theo find a silver treasure box. And within the box, a prophesy."
The Warlock Diaries vol. 1 (Avalon: Web of Magic), by Rachel Roberts. A manga adaptation of the Web of Magic novels. "Teenage mages, Emily, Kara, and Adriane have their hands full monitoring the portal at the Ravenswood Preserve. The portal has become the "Grand Central Station" of the Magic Web, with magical creatures and animals stopping by on their way to otherworldly destinations. But matters become really complicated when a new student, a handsome young warlock named Donovan, shows up at Stonehill High. When monsters start attacking Ravenswood looking for Donovan, the mages realize he may be trouble. But Donovan shows them what he has brought, a fairy map with the portal sequence that will lead the mages right to Avalon, the source of all magic."
The Twilight Zone: Deaths-Head Revisited, by Rod Stirling and Mark Kneece, illustrated by Chris Lie. "[This] entry in the Twilight Zone series of graphic novels follows former SS captain Gunther Lutze as he returns to Dachau to visit the concentration camp where he murdered hundreds decades earlier. He is soon met with the ghosts of the persecuted, who try him for his crimes."
And another Twilight Zone graphic novel, The Twilight Zone: The Midnight Sun (Rod Serling's the Twilight Zone).
Gorgeous, by Rachel Vail. "...when the devil shows up and offers to make her gorgeous, Allison jumps at the chance to finally get noticed. But there's one tiny catch, and it's not her soul: The devil wants her cell phone. Though her deal with the devil seems like a good idea at the time, Allison soon realizes that being gorgeous isn't as easy as it looks. Are her new friends and boyfriend for real, or do they just like her pretty face? Allison can't trust anyone anymore, and her possessed phone and her family's financial crisis aren't making things any easier. Plus, when she finds out that she might be America's next teen model, all hell breaks loose. Allison may be losing control, but how far is she willing to go to stay gorgeous forever?" Sequel to Lucky.
Hunger: A Gone Novel, by Michael Grant. "It's been three months since everyone under the age of fifteen became trapped in the bubble known as the FAYZ. Three months since all the adults disappeared. Gone. Food ran out weeks ago. Everyone is starving, but no one wants to figure out a solution. And each day, more and more kids are evolving, developing supernatural abilities that set them apart from the kids without powers....But a larger problem looms. The Darkness, a sinister creature that has lived buried deep in the hills, begins calling to some of the teens in the FAYZ. Calling to them, guiding them, manipulating them."
Jennifer's Body, by Audrey Nixon "...after that night in the woods, Jennifer was different. She looked different. And then the killings began. . . .A lot of people ask me if I'm sorry I did it. I'm only sorry I didn't do it sooner." Jennifer has been possessed. Based on the screenplay of the movie by the same name.
Killer Pizza, by Greg Taylor. "Learning to cook pizzas is one thing, but killing hideously terrifying monsters? That’s a whole other story. Still, if Toby quits Killer Pizza, will monsters take over his town?"
Once Dead, Twice Shy (Madison Avery, Book 1), by Kim Harrison. From the Booklist review: "Madison is dead. After she fled her prom with a mysterious guy and ended up in a crashed car—only to survive and then be struck down by this guy’s magical sword—she has existed in a curious state of purgatory. She still walks around, interacts with others, eats, and sleeps, only now she does so in the company of Barnabas, a light reaper—a kind of angel who fights off dark reapers trying to harvest the souls of people about to make fate-altering decisions."
The Sorceress (The Secrets of the Immortal Nicholas Flamel), by Michael Scott In the third book of this series, Nicholas Flamel, the immortal alchemyst, and human twins Sophi and Josh, are "confronted with a demonic bounty hunter that immortal magician John Dee has sent their way. At the same time, Dee's occasional cohort, Niccolo Machiavelli, decides to focus his energy on Perenelle Flamel, the Alchemyst's wife, who has been imprisoned at Alcatraz since the beginning of the series. In this book, Perenelle gets a chance to show off her sorcery and resourcefulness, fighting and forging alliances with ghosts, beasts, and the occasional Elder to try and find a way out of her predicament and back to Flamel."
Vacations from Hell, by Libba Bray, Cassandra Clare, Claudia Gray, Maureen Johnson, & Sarah Mlynowski. "...supernatural tales of vacations gone awry. Lost luggage is only mildly unpleasant compared to bunking with a witch who holds a grudge. And a sunburn might be embarrassing and painful, but it doesn't last as long as a curse. Of course, even in the most hellish of situations, love can thrive. . ."