What tools do you use to test applications?

Ethereal : Capturing the traffic http://www.ethereal.com/distribution/win32/
Nikto : Comprehensive tests against web servers for multiple vulnerabilities http://www.cirt.net/nikto2
Nessus : Remote vulnerability scanner/fingerprinting the OS http://www.nessus.org/nessus/
Winhex : Check Memory Contents http://www.winhex.com/winhex/index-m.html
WebScarab : Web PRoxy: http://www.owasp.org/index.php/Category:OWASP_Project