If you liked Challenger Deep by Neal Shusterman, you might want to try these books:
Crazy by Han Nolan
Fifteen-year-old Jason has fallen upon bad times—his mother has died and his father has succumbed to mental illness. As he tries to hold his crazy father and their crumbling home together, Jason relies on a host of imaginary friends for guidance as he stumbles along trying not to draw attention to his father's deteriorating condition. Both heartbreaking and funny, CRAZY lives up to the intense and compelling characters Han Nolan is praised for. As Jason himself teeters on the edge of insanity, Nolan uncovers the clever coping system he develops for himself and throws him a lifeline in the guise of friendship.
All The Bright Places by Jennifer Niven
When Theodore Finch and Violet Markey meet on the ledge of the bell tower at school, both teetering on the edge, it's the beginning of an unlikely relationship, a journey to discover the "natural wonders" of the state of Indiana, and two teens' desperate desire to heal and save one another.
(Told in alternating voices)
Perfect by Natasha Friend
Thirteen-year-old Isabelle Lee's family is reeling from the recent death of her beloved father when little sister April (aka Ape Face) finds Isabelle purging her dinner in the bathroom. Isabelle is sent to group therapy for her eating disorder, where she is shocked to discover that her school's most "perfect" and popular girl, Ashley Barnum, is also bulimic. Ashley is delighted to find a like-minded classmate, and she takes the previously unpopular Isabelle under her wing, inviting her to the exclusive lunch table and to sleepovers where they consume and then expel mountains of food. Isabelle's grief and anger are movingly and honestly portrayed, and her eventual empathy for her mother is believable and touching. Through Isabelle's wry tone and clear eye for hypocrisy, Natasha Friend elevates what could have been just another problem novel to a truly worthwhile read of great interest to many girls.
Unlikely Hero of Room 13B by Teresa Toten
Marry Robyn Plummer.
The instant Adam Spencer Ross meets Robyn Plummer in his Young Adult OCD Support Group, he is hopelessly, desperately drawn to her. Robyn has a hypnotic voice, blue eyes the shade of an angry sky, and ravishing beauty that makes Adam's insides ache. She's also just been released from a residential psychiatric program—the kind for the worst, most difficult-to-cure cases; the kind that Adam and his fellow support group members will do anything to avoid joining.
Adam immediately knows that he has to save Robyn—must save Robyn—or die trying. But is it really Robyn who needs rescuing? And is it possible to have a normal relationship when your life is anything but?
Maybe One Day by Melissa Kantor
A person's whole life, she's lucky to have one or two real friends—friends who are like family. For Zoe that someone is Olivia. So when Olivia is diagnosed with leukemia Zoe is determined to put on a brave face and be positive for her best friend.
Even when she isn't sure what to say.
Even when Olivia misses months of school.
Even when Zoe starts falling for Calvin, Olivia's crush.
The one thing that keeps Zoe moving forward is knowing that Olivia will beat this, and everything will go back to the way it was before. It has to. Because the alternative is too terrifying for her to even imagine.
Invisible by Pete Hautman
It's clear from the start that there's something not right about the relationship between narrator Doug Hanson and his best friend, Andy Morrow. Doug, a self-proclaimed nerd, is primarily interested in building a matchstick replica of the Golden Gate Bridge for his model railway town. Andy is popular, a football player and actor. But the boys live next door to each other and talk from their bedroom windows at night.
In an almost robotic voice that still manages to be intensely insightful, Doug takes readers to his school, where he is mocked and eventually beaten, and to his neighborhood, where he turns into a Peeping Tom watching school star Melanie Haver undress. Hautman does a superb job of crafting the odd sanctuary that is Doug's mind. But Doug's defenses are crumbling, and the secret he's been keeping about Andy is oozing through the cracks. The truth about Andy won't come as a surprise, but there are some unexpected plot turns here, and the chilling but ambiguous denouement is definitely unsettling.