I'm slowly (I work 4 days a week and take care of my son while my wife's in school) writing a young adult novel about a guardian angel, and I was hoping you guys could help me out.

What other titles have you guys either read or heard about that have guardian angels in them? Young adult preferred, of course, but I'll take anything that's got stuff about angels, really. I'd like it to be fiction, but if you've got a really cool recommendation of non-fiction, that'd be sweet, too. I want to start reading in the area that I'll be writing in, and haven't had much time to really study up on just what's out there. Combine that with the atrocious search engine of my local library, and I doubt I'll find much, so I'm turning to you.

PS, you guys rock.