[BrandonMarc]

Have you ever used McAfee Secure (formerly known as HackerSafe)? Security scanning service for websites, looks for 1000's of different vulnerabilities, rates by severity, provides a badge. It's actually quite extensive (and not cheap), but it would be worth researching and seeing what you can emulate.

Their reputation is such that the credit-card vendors trust their results for PCI compliance testing ... a major thing in e-commerce and online payment.

I believe a special filename & contents is required somewhere, to prove you do indeed own the site you're scanning.

Perhaps you're not interested in competing with them yet, but it's something to consider.