13 Little Blue Envelopes -- Maureen Johnson

As I'm pretty much the last person on the planet to read this book, I'm not going to write an in-depth synopsis. 

Just know that the book is well-written, smart, sensitive, funny, has likable, realistic and well-rounded characters, and will appeal to fans of the Traveling Pants books.  (It may appeal to non-fans as well -- I really, really enjoyed 13 Little Blue Envelopes, while I was only 'eh' on Traveling Pants.  Also, while there is some talk about sex, Ginny doesn't, say, have sex with her soccer coach or anything.)

Although the major plot structure surpassed my personal suspension-of-disbelief limit, I doubt that'll be an issue for most teen readers -- I think a lot of them will wish they could have an adventure just like Ginny's.

(My only major complaint is the cover art.  That girl is just SO NOT GINNY.  AT ALL.  Her posture/stance, her clothing -- everything about her is just wrong.  And where's her backpack?  Sheesh.  )