September's recommendation: Avalon High, by Meg Cabot.
I picked this book up while on a concerted research campaign that had me reading a bunch of young adult urban fantasy. Having plowed through more than ten of those books, I can say with confidence that Meg Cabot is the best author I've yet found, with clever ideas and a fun writing style that extend over several different series. She is not a one-trick pony.
So consider that a general recommendation for Meg Cabot as a writer. If I had to pick one of her books to advertise specifically -- and obviously that's what I'm doing, here -- it's Avalon High.
It's an odd choice, because Ellie might be the least immediately sympathetic main character I've yet found in Cabot's books. Which is not to say she's a bad character; just that her opinions run almost directly counter to my own. You see, the story begins when Ellie's professor parents go on sabbatical, transplanting her to another city for a year. Both of them are medievalists; her father's studying an old sword in a museum, while her mother is writing a book about the Lady of Shallot. And as far as Ellie is concerned, these are among the most boring topics in the entire world.
You might understand why I find this hard to sympathize with.
But if Ellie liked Arthurian material, she would figure out too quickly that all is not normal at her new high school. You noticed the book's title, right? Her school is Avalon. There's a star jock named Lance. And a popular cheerleader named Jennifer. And Ellie's hatred for the Lady of Shallot comes from the fact that she was named for the lady in question, Elaine of Astolat.
If the book were just a retelling of Arthurian legend by way of a modern high school, it would hold limited interest for me. Fortunately, Cabot knows better than to stop there. Yes, some of the students may be reincarnations of people out of legend -- but that's part of a larger pattern that reminds me of nothing quite so much as Susan Cooper's The Dark Is Rising series. There is a larger conflict, that plays itself out over and over again, and each time it's different. And this time, things may be changing radically, bringing a hope that has never existed before.
The one oddity here is that while Avalon High feels like the beginning of a series, the only continuation I can find on Cabot's website is in manga form. I'm not sure what's up with that -- whether it was always planned that way, or Cabot's fiction publisher wasn't interested in picking up the later books -- but it means that, while the first book is reasonably satisfying on its own, if you (like me) want more, you may have to go to the manga section of the store to find it.