Here are three books that I put down more than a month ago, and am not sure I'll ever get back around to. If you've read any of them, you should let me know your thoughts!
Bittersweet by Sarah Ockler is a book I began all the way back in January of 2014 - it's been a long time. I probably will get back to this one, but it might take some time as I will have to reread the half of the book I got through, in order to refresh my memory.
A World Without Princes by Soman Chainani is the one on this list that I am least likely to continue. It never hooked my interest, and felt almost like a repeat of the same book with a slightly different conflict - like the characters got over the strict stereotypes of good and evil only to move onto the conflict between boys and girls. I can already predict how it will end. (If you have anything good to say about this that might convince me to read, please share! I would like to convince myself to finish if only because I paid full price for the ebook.)
The Song of Achilles by Madeline Miller is one that I put down much more recently, back in February. It's the one on this list I'm most likely to get back to reading, although I am not in a huge rush to get back to it, since I know how it ends.