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.

gilles66

Need to know which template is used by WordPress to display your pages in the front office ? 
This plugin simply does this.
Show the name of the php file of your theme used to display the current page.Need to know which template is used by WordPress to display your pages in the front office ? 
This plugin simply does this.
Efficient and very easy to install, it will show you in the admin bar the name of the php file currently used to display the current page. 
The color of the text is different regarding the origin of the template(the theme, a parent theme, or a plugin) 
(icon author :http://www.megaicons.net/iconspack-1096/45043/)

which template file

Show the name of the php file of your theme used to display the current page.

Debogger vs which template file