Give it a try, for $1 dollar you get 5 books, for $8 dollars you get 7 books more, and for $15 dollars you get 16 books in PDF, mobi or ebook. They can also email them to your kindle ;-). Did I mentioned they are DRM free? ?

Get a bundle of Unix ebooks and support charity!

Source: Humble Book Bundle: Unix presented by O’Reilly (pay what you want and help charity)