My friend Laurel has bought me a new book, it's called Ultra Marathon Man.
This is the website: http://www.ultramarathonman.com
If the cover is anything to go by, this dude is hardcore.
I'm almost done with The Runner's Handbook by Bob Glover, which was really good:
http://www.amazon.co.uk/Runners-Handbook-Best-selling-Beginner-Intermediate/dp/0140469303