Halo by Alexandra Adornetto
Something I notice (and obsess over) on a lot of covers is hair. And wings. And pretty fonts. And this book has all of them. It's kind of amazing.
Seriously, though, I love everything this cover has for us. The silhouettes are beautiful, the wings are practically breathtaking, and the fancy edges around the title make it sort of like a logo, which makes it easily recognizable on the other books in the series.