The Blue Girl is about a girl named Ingrid, who moves from Tyson to Newford (or something like that... I can't remember the exact name), from gang to relatively normal life. The book is told from three different points of view: Ingrid, her best (and only) friend Maxine, and the ghost boy who has a crush on the aforementioned Ingrid; and from two different time periods: then and now. In then, the three characters tell of Ingrid's year in high school in Newford. In now... things get a bit more creepy. The supernatural begin to haunt Ingrid's dreams, along with Pelly, her abandoned imaginary friend.
Ingrid is an amazing character – she develops perfectly from beginning to end, retaining her quirky and fun view on life throughout the book. Maxine changes, too, almost more so than Ingrid. If I write any more, I'm going to give away the ending.
He (Charles de Lint) has written a few other books, and a couple collections of short stories. All that excellent new genre, urban fantasy, and all amazing. Check him out!