Simon Prosser

Debugging tool for theme authors and reviewers.
This tool intercepts all debug information and prints it all out neatly into the footer. It also checks each page for W3C validation. 
This plugin is released as a tool to aid the development of themes and plugins for WordPress and can be used to aid debugging your theme before submission to the themes directory.

Debogger

Debugging tool for theme authors and reviewers.

bluenestbryan

This plugin adds the name and path of the theme (template) file used to generate the html page into the page’s source as a comment. It will also add the name of the header, footer and sidebar if they are included.
This is useful for debugging and seeing what template file generated a page.
To use, activate, then reload any open pages. In the HTML comments, you can search for “TEMPLATE INFO” to see the added comments with the names of the template files included.

Template File Name Debugger

Add the name of the theme (template) files used to generate a page into the page's
source as a comment.

Debogger vs Template File Name Debugger