Several weeks ago, a contributor for the Wall Street Journal wrote an article entitled Darkness Too Visible . The author's complaint was that contemporary YA literature, aimed at the broad range of 12-18 year-olds is inappropriate for it's heavy inclusion of "explicit abuse, violence and depravity".
Then the internet blew up. Several interesting responses have come from NPR, one from pop culture expert Linda Holmes , and another interview  with a YA librarian, YA authors, and the original author of the WSJ article.
Without rehashing too much, I found some of the titles mentioned in the debate interesting. In the original article, The Absolutely True Diary of a Part-Time Indian  by Sherman Alexie is mentioned in the "too dark" camp. Yes, this book has it's harsh moments and may be best recommended to slightly older teens, but it is also a beautiful, intelligent and hopeful coming of age story. The WSJ article also has a list (on the side) of titles that they "can recommend" and include the post-apocalyptic Z for Zachariah  by Robert C. O'Brien which I read as a teenager. It was nightmare inducing at the time and still gives me the chills - 20 years later.
As an adult reader of YA fiction, I generally find there to be a wide variety. With only a few exceptions, dark themes seem to be mostly handled in a constructive way. If that isn't enough - sweet titles still exist!
I recently read and highly enjoyed Little Blog on the Prairie  by Cathleen Davitt Bell - super funny and a perfect summer read - and for even more (generally) happy girly fun adventure, try the Gallagher Girls series  by Ally Carter.