Are there any good download managers for books?

I have an iPod Touch and I installed the Download Manager App and it works great for YouTube videos, but I can’t seem to find a good website that’ll let download books. It says that the compatible files include PDF files. Is there a site where it would make downloading a book more easily. Preferably, is there a link that would direct me to a place where downloading is made easy and not a task?

(btw I’m looking for a book called “The Sorcerer’s Stone: The Beginners Guide To Alchemy.)