Albert Bertilsson

This plugin gives you an overview of page templates in your site. You get both an overview of all templates and how many pages they have. You also get a detailed view of all the pages using a specific template.
Usage for this can be to identify unused templates and to find pages using specific templates to change them in some way.

Template Usage

Template Usage gives you a simple overview page of all page templates in your site, allowing you to easily find pages using a specific template.

cleanscript

A very simple plugin that provides information about the Custom Page Templates available in the theme: What they are, which are not used and where the used ones are used, selectively.
Main features: 
Available page templates list 
Unused page templates list 
List of page templates with checkboxes that output when submitted the links where they are used

Cleanscript – Page Templates Info

Find information about your page templates. What they are, which are not used and where the used ones are used, selectively.

Template Usage vs Cleanscript – Page Templates Info