Rigel Kent Security finds the following Tools and Resources to be of value :

IDA Pro Disassemblerwww.hex-rays.com/idapro/
Immunity Debugger www.immunitysec.com/products-immdbg.shtml
Immunity CANVASwww.immunitysec.com/products-canvas.shtml
Metasploitwww.metasploit.com
Burp Suitewww.portswigger.net
Fiddlerwww.fiddler2.com
SOAP UI www.soapui.org
NIST Computer Security Resource Centercsrc.nist.gov
Open Web Application Security Projectwww.owasp.org