Easily apply templates to your category archive pages and posts with this plugin.
Valid templates are files placed your theme folder with the following code at the beginning of them:
For Post Templates: Template Name: Blog Template
For Archive Templates: Archive Template: Blog Template
Through this plugin’s options panel, you can choose which templates are applied to categories and posts. Even choose their priority over one another. You can even apply a template to an individual post. 
Please <a href="http://aarongloege.com/blog/web-development/wordpress/plugins/wordpress-plugin-category-templates/#respond" rel="nofollow ugc">report any bugs</a> you come across.
Enjoy!

Category Templates

Give your categories and posts their own individual templates.

Jamie O

This plugin makes category templates be selectable by drop-down list from the manage > categories screen of the admin console. It makes the selection / use of category and post templates as easy as page templates. It also includes configuration options that allow you to configure whether sub-categories inherit templates from their parent if none are specified.
Features:
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You can now use one category template for multiple categories without identical copies of the category-##.php
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All category / post templates and settings are relative to the current theme applied to WordPress
</li>
<li>
If you select a different theme, the entries will remain in the database in case you want to revert back.
</li>
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If you delete a category, all records (regardless of theme / version) will be deleted.
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The Sub-Category Inheritance option applies for both category templates and post templates.
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Now supports parent / child theme configurations.
</li>
</ul>

Idealien Category Enhancements

Modification to the category and post template logic to behave like pages (selectable through admin)

Category Templates vs Idealien Category Enhancements