Unix for the Beginning Mage is really good book that explains the concept of Unix is a very interesting way. It is available both for free as a PDF file and as a hardcopy version.
Even though I have been working with Linux/Unix systems for a while I enjoyed reading it and a more advanced version of the book is in the works.
In the mean time check out the beginner’s version.
Visit: UnixMages.com
– Suramya