I'm not a web developer, so I really have no idea if this will be helpful or not...
I was looking for a method of quickly checking the website for broken links or any common errors that might put off a new user to the website. I found Black Widow 5 at:
http://softbytelabs.com/us/downloads.html
Looks to me like this will scan for and report on errors that the website has as well as help identify which portions of the site are visible to someone snooping around.
<shrug>
BTW- I like the default 404 error message that you have- "The minions of the underworld have struck again! The page you requested could not be found"
Terrin