Ripper, by Stefan Petrucha

Orphan Carver Young has some general fantasies about becoming a detective, and devours novels and stories about  great sleuths, as well as serialized and sensationalized mysteries.  When ex-Pinkerton Detective Albert Hawking, cranky, contentious, eccentric, brilliant, and crippled, offers to take Carver on as an apprentice to share all he knows, Carver is ecstatic, even though it means living (for a reason I never really understood) in a private floor at the top of a mental institution, and getting more questions, half-hints, and criticism from Hawking than direct answers.  Carver's first and main "case" is to figure out the identity and possibly location of his father based on a scrap of a letter sent to the orphanage many years before.  As part of this Hawking introduces him to the "New Pinkertons", an underground (literally) and top-secret detective agency endowed by Alan Pinkerton upon his death. Hawking was head of the agency until his injuries forced him to give the reins to another former Pinkerton agent, Tudd, who is devoted to "gadgets" and buys many, many new mechanical, electrical inventions to help the secret agents with their investigations, and who is obsessed with catching a murderer, convinced it is the return of Jack the Ripper.

Tempest by Julie Cross

19-year-old Jackson Meyer can time travel.  Not much, usually just back a few hours or days.  And when he does go back, nothing he does actually impacts the future - no one remembers interacting with him if it happened on one of his jumps, if he hurts himself he isn't seriously damaged when he gets back, and if he does something on one of his jumps, like break a window, that thing is undone when he gets back to the present.  It's not really serving a purpose, but he's having fun experimenting, and keeping it a secret from everyone but his science genius friend who is helping him figure out why it's happening and how to use it.  At least it is all fun until some people who also appear to be able to "jump" back in time show up at his girlfriend's college dor, attempt to kidnap Jackson, and kill his girlfriend in the struggle.  Now Jackson has jumped back 2 years, farther than he's jumped before, and no matter how hard he tries, he can't get back to his "real" time.  And the Enemies of Time are still after him.

Ruby Red by Kerstin Gier

1st in Ruby Red series.  Sequel is Sapphire Blue.  First published in Germany.

Gwen is 16 and lives with her mum, siblings, grandmother, aunt and cousin in an upperclass London neighborhood.  Her extended family doesn't pay much attention to her, focused on her cousin, believed to be the carrier of the time-travel gene that runs through her family and sure to show up very soon in the form of an abrupt trip to somewhere in the past.  But all is not as it seems.  Since a mathematical formula had worked out that Gwen's real birth  date was the birth date of the next time traveler, and her cousin was also born that day, Gwen's mum and (late) father secretly falsified her records to indicate Gwen was born the day before, allegedly in the hopes that she would be able to live a normal life (and since she was born at home with a midwife, no one was the wiser.

Prepare to Die by Paul Tobin

Despite being at their mercy, Steve Clarke, aka superhero Reaver, is inexplicably given a boon by arch-nemesis Octagon and his cadre of supervillains, Eleventh Hour - instead of killing him outright, they grant him 2 weeks to take care of his affairs before he reports back to them to fight to the death.  Steve uses the two weeks to come to grips with how he became a superhero in the first place, the loss of superfriends, his own moral ambiguity at times, and to reunite with his high school love, the girl who got away (or was pushed away due to Steve's unanticipated mutation caused by a chemical spill which transformed some of the cars occupants and killed others).

The Book of Blood and Shadow by Robin Wasserman

Nora has a pretty good life - yes, her brother is still dead and her parents are still withdrawn into their own self-absorbed worlds, but she has made a new family of sorts, with bright, charming, boy-wonder Chris and his lovely, capricious girlfriend Adriane as her best friends, and moody, quiet, scholarly Max as her boyfriend.  She also has an engrossing translation project for a local professor to strengthen her link with Chris and Max - while they work on translating the "important" parts of an ancient mystical document the professor is obsessed with, Nora translates late 16th century letters from a young woman, stepdaughter to a great magician - busy work to the professor, but more and more fascinating to Nora.  When her translation of the letters leads to a new discovery, she never expects it to end with the professor insane, Chris dead, Adriane catatonic and Max gone and branded a murder...but that's what happens.

Insurgent by Veronica Roth

Sequel to Divergent

Tris, now on the run as war erupts, attempts to figure out what information is so vital, or so dangerous, that some factions would destroy others just to contain it.  

Divergent by Veronica Roth

In dystopian Chicago, society has been divided into 5 factions, each dedicated to cultivating a certain value:

• Amity (the peaceful)
• Candor (the honest)
• Abnegation (the selfless)
• Erudite (the intelligent)
• Dauntless (the brave) 

Scarlet by A.C. Gaughen

The early days of the Robin Hood story, told from the perspective of "Will" Scarlet.  Known to Robin, John, and a few others as just Scarlet, she is a young woman posing as a young man after running away from an arranged marriage.

Star Crossed, by Elizabeth Bunce

Escaping from Green Men soldiers after a botched theft results in her partner's death, Digger convinces a boat of young nobles to help spirit her away, thinking they are helping "Celyn" escape from convent school.  Willing to leave the city of Gerse behind for awhile, Celyn becomes a maid to one of the nobles, a younger girl named Merista who is about to be presented to the marriage mart, and goes with Meri to reunite with her parents, exiled for the last several years for their part in a plot to overthrow the king and the corrupt church. 

Crossed, by Allie Condie

Sequel to Matched.

Three Thieves series, by Scott Chantler

Book 1:  The Tower of Treasure:  Dessa, a 14-year old acrobat in a traveling circus, gets lured into helping Fisk, the scheming troupe juggler, and Topper, the gentle strongman, rob the royal treasury when she decides it will help her learn more about the mysterious man who kidnapped her twin brother several years before.  Caught in the act, they are able to escape from the tower prison but are followed by the grasping Queen's honorable, duty-bound captain of the guards, Drake.  Graphic novel, good for older elementary and middle school - mysteries, fantasy, adventure readers.

  Book 2:  The Sign of the Black Rock:  After escaping from the royal prison, Dessa, Fisk and Topper flee to the coast, where they seek shelter at an inn from a ferocious storm.  The Queen's Dragons and Captain Drake aren't far behind, though, and soon the thieves are hiding from the guards, held captive by the scheming innkeeper, and set free by his abused and silent wife, who also shares more information with Dessa about the sorcerer who kidnapped Dessa's brother and scarred the innkeeper's wife in an attempt to cut out her tongue before she could tell anyone about the spell book and odd word she discovered in his room.

Ready Player One, by Ernest Cline

Lots and lots and LOTS of geek and pop culture references from the 80's, as a teenage boy and his cohorts/competition attempt to solve puzzles in an online game that will determine who controls the internet in a futuristic society that lives mainly online.  Full summary from the publisher after the break.  Good for advanced teens and adults interested in the tagged subjects.  2011.

Sweet Venom by Tera Lynn Childs

The Agency: A Spy in the House, by Y.S. Lee, Bk 1

Ninth Ward, by Jewell Parker Rhodes

Dealing with the days leading up to and immediately after Hurricane Katrina, through the eyes of a 12 year old girl living in NOLA's Ninth Ward with her 82-year old caretaker, Mama Ya-Ya.  Allows the reader to see the neighborhood and the life through the eyes of a bright, creative child who sees ghosts, believes in signs, loves math and words and learning and longs to build bridges when she grows up.

The Rise of Renegade X, by Chelsea M. Campbell

Damien Locke is all set for his 16th birthday - it's the day his life of crime officially begins.  It's basically a technicality - Damien's mom is the mad scientist Mistress of Mayhem, he is a shoe-in for Vilmore Academy, the ultimate school for teenage supervillains and he's already got his supervillain name picked out: Midnight Marauder.  But in Golden City, all supers have a letter appear on their hand on their 16th birthday to make it official - H for heroes and V for villains.  So imagine Damien's surprise when his V doesn't show up, but neither does an H; an X appears instead.

Paranormalcy, by Kiersten White

One in a spate of paranormal-themed YA books, this one held my interest more than many of the others I've read lately.  Evie is a teen who has been fostered with the International Paranormal Containment Agency since she was 8 years old, working for them during that time as the only person able to see through any glamour from any paranormal.  It's not breaking new ground in terms of content or teen angst, but it does have some nice "surprises". 

Only the Good Spy Young, by Ally Carter, Bk 4 in the Gallagher Girls series

In the previous three books in the series Cammie aka Chameleon Morgan has found out how serious being a Gallagher Girl is.  In the beginning it was fun knowing that she was a spy-in-training, sneaking out to meet a townie boy in Book 1 and using their special skills at detection, evasion, invention and deception to learn more about the mysterious boys from Blackthorne Academy in Book 2. 

Incarceron, by Catherine Fisher

Finn is a "cell-born" member of a Scum gang in Incarceron, the living prison with millions of electronic eyes and torture chambers, designed to recycled and re-use everything, even the people who are imprisoned there.  Finn remembers nothing before waking up in a cell, apparently remade from DNA of others who died, but his flashes of memory of the outside world convince him that he belongs outside.

One Night That Changes Everything by Lauren Barnholdt

Eliza is looking forward to a quiet night watching movies with her best friends while her parents are out of town, but a club of boys from her school, including the ex-boyfriend that only dated her as initiation into the club, use her notebook of secret things to blackmail her into doing stunts around Boston. Includes under-age drinking, references to drugs and sex that might make some teens (and unparents) uncomfortable, but the overall message doesn't glorify any of them. The relationships with best friends are depicted pretty realistically (both friends get distracted by their own concerns - other friends, boys, etc. - but pull together for Eliza when she needs them most. A touch of romance, a supportive relationship with her older sister, and the thrill and danger of staying out all night will appeal to teen readers, probably of the female variety.

My recommendation - 9th grade and up.