Front end developer Philip Walton has created a customizable HTML tool to verify code.
"HTML Inspector is a code quality tool to help you and your team write better markup. It's written in JavaScript and runs in the browser, so testing your HTML has never been easier".
Why use this instead of the W3C validator? Because it's customizable both in terms of what it checks and being able to write custom rules.
See his post on http://philipwalton.com/articles/introducing-html-inspector/
And the source/download on Github.