Syngress has been fast and furious in the publishing of security books as of late.
Just got two new pen test books from them:
The Basics of Hacking and Penetration Testing is meant as an introductory text and covers all of the requisite tools such as Backtrack Linux, whois, Nmap, Nessus, Metasploit, Netcat and more.
The Penetration Tester's Open Source Toolkit is more of an advanced title.
Both look to be good references.