Hagakure may be familiar to anyone who has seen the film 'Ghost Dog'. It contains anecdotes relating to the way of the samurai, but can be (unfairly) summarised as follows: the way of the samurai lies in death, death must be contemplated on a daily basis, even the slightest example of disrespect should be met by immediate and fatal remedy. In particular, seppuku (hiri kiri) is the noble and glorious end to virtually all anecdotes.
It is a remarkable book, and probably the most interesting of the Samurai guides (eg Book of Five Rings). However, it should be remembered that Hagakure was considered exceptionally fundamentalist when it was written (17th century) and was disapproved of due to its overemphasis on death.
It was also a favourite text of Yukio Mishima, which if you know about Mishima, tells its own story.