Here is a link that has some good resources.
First, I would suggest any books that are sold by the Vendor of your OS. Like Sun and HPUX both have books for OS Specific topics.
Also, some good books are:
"UNIX in a Nutshell" by O'Reilly.
"Sed & Awk" by O'Reilly
"The AWK Programming Language" by Aho, Kernigan, Weinberger
"TCP/IP Network Administration" by O'Reilly
For a beginner this next book is a MUST HAVE!!!!!!!!!
Another AWESOME book, sometimes referred to as "The Red Book". I think it is now a 3rd edition for around $65, but I just found a 2nd ed for $6! at a used book store. Shouldn't be much difference.
"Unix System Adminstration Handbook" by Nemeth, Snyder, Seebass, Hein
That should keep you busy for a few years!!!