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.

Mike Schinkel

NewClarity

This plugin does what it names says; it omits page templates from the parent theme from the template dropdown when you are editing a “Page” in the WordPress admin.

Omit Parent Theme Page Templates

Omits Parent Page Templates from the "Page" edit screen in the WordPress admin.

Template Usage vs Omit Parent Theme Page Templates