I can't really suggest any books for Linux since I don't know any (taught myself through learning-by-doing and pestering those who introduced me to it
![Wink Smilie](https://www.unix.com/images/smilies/wink.gif)
). But I can, with a clear conciseness, recommend most books published by O'Reilly and Addison-Wesley.
Other than that it's mostly online resources, like
this or
this, forums, newsgroups, or your local LUG (Linux User Group)