"The Ranger's Apprentice" series. The first book is entitled "The Ruins of Gorlan".
This is not a cross genre series or anything, but having just finished the first book, I have to say that this is a really cool series.
I like the world that John Flanagan has created and the book was a great read. It's technically for teens so it was a short read as well.
I think it works well for adults or teens. I am a big fan of Rangers, Knights, monsters and the like and this book has plenty of all of that. I can't wait to pick up book 2!
Note - there was a movie announced in 2008. Recent funding issues have slowed it down, but John Flanagan says it is still a go.