I'm always surprised by the folks I meet at conferences who want to write YA, but have not READ much of it.
I read at least as much YA as I do adult material, and guess which I usually like better?
So where to start? I'm glad Shannon brought up the Popular Paperbacks by YALSA. That particular award is great as it organizes best books in a particular genre, like spy stories. So not only will folks be looking at it if it wins after the announcement but any year in the future when they have a teen who wants spy stories. As a librarian, I am constantly looking at the genre lists for that award. I've used the 'Books That Won't Make You Blush" many times when I have a parent who wants teen books that are not too mature for a younger teen reader.
If you want to write for YA, find out what other awards are out there, and which ones are chosen for which. Try looking at www.ala.org/YALSA at awards and booklists.