Sacred:Book of the Seraphim
There is one book in all of Ancaria that's extremly rare and a most interesting find. It's the Book of the Seraphim and can only be gotten if you're playing the Seraphim character.
In the Oasis of Ahil'Tar, there is a quest giver named Gunther the Seer who had a vision of a nightmarish demon hanging out in the desert and would like you to go check it out. If you're playing any other class, you simply go down there, kill the demon and his minions and then return to the Oasis to have a chat with Gunther for your reward.
However, if you are playing a Seraphim, you will find another Seraphim in the pile of dead bodies. She is likely the same one you rescued previously near Bellevue. She will tell you that "they lied" just before she dies. At which point, she will drop the book and what amounts to being the only lightsaber in the game.
The book is very interesting - if for no other reason than it tells the story of the origin of the Seraphim.