I'm currently reading Mark of the Thief by Jennifer A. Nielsen and earlier this month she revealed the cover for the next book in the series.
please read her blog post on the book.
I will say this though, the cover is beautiful. Whereas the first book's cover didn't wow me (i.e. not enough contrasting colours), this one does.
It's real fancy. I'm not even done the first book yet but I'm excited.