A very good source for Unix Books
The Art Of Unix Programming by Eric Raymond
This book will attempt to capture the engineering wisdom and philosophy of the Unix community as it's applied today -- not merely as it has been written down in the past, but as a living "special transmission, outside the scriptures" passed from guru to guru. Accordingly, the book doesn't focus so much on "what" as on "why", showing the connection between Unix philosophy and practice through case studies in widely available open-source software.
You probably never knew that there were diapers being sold under the UNIX trademark...
An extensive list of commands and tasks that are reasonably useful to fairly advanced users, and with some "dialect" translations for common flavours (e.g. - several Linux flavours versus FreeBSD).