The Malware Analysts Cookbook is unique is that it discusses (and includes on the DVD) several customized tools based on http://yara-project.googlecode.com
One of them is simply a packer ID file for yara.
Another great tool is called pescanner.py.
Both of these tools are discussed here -- http://www.zonbi.org/archives/495 -- and I found another cool blog that's totally unrelated here -- http://lvdeijk.wordpress.com/2011/02/21/closing-the-loop/ -- that I'm including for fun.
I am also a fan of the MANDIANT Red Curtain tool for analyzing potential malware.