The DUFF by Kody Keplinger
From Goodreads: Seventeen-year-old Bianca Piper is cynical and loyal, and she doesn't think she's the prettiest of her friends by a long shot. She's also way too smart to fall for the charms of man-slut and slimy school hottie Wesley Rush. In fact, Bianca hates him. And when he nicknames her "Duffy," she throws her Coke in his face. But things aren't so great at home right now. Desperate for a distraction, Bianca ends up kissing Wesley. And likes it. Eager for escape, she throws herself into a closeted enemies-with-benefits relationship with Wesley. Until it all goes horribly awry. It turns out that Wesley isn't such a bad listener, and his life is pretty screwed up, too. Suddenly Bianca realizes with absolute horror that she's falling for the guy she thought she hated more than anyone.
I really fancy reading this one and have seen some really good reviews for it! It's published September 7th 2010 (US)