HTML Tidy Online

"HTML Tidy is a tool for checking and cleaning up HTML source files. It is especially useful for finding and correcting errors in deeply nested HTML, or for making grotesque code legible once more.

This online version enables you use it without installing the client tool on your PC. More information about HTML Tidy is available from the original W3C page, and you can download a local copy of it from the SourceForge project page."

link via martin at Geekfishing Blog