Rob Saurini

If you have more than one category associated with a post, how do you tell which category takes precedence? This plugin gives you the ability to promote the category to the main one on the post edit page.
This gets stored in post meta for later use. Soon, I will add some simple functions that will allow you to get the main category on the front end.
Use
<ul>
<li>You can use the shortcode [rs_print_main] inside the post to print out the category title.</li>
<li>In the theme, you can use rs_get_main_category_id( $post_id ) to return (not print) the id of the main category.</li>
</ul>

RS Simple Category Selector

Gives you the ability to promote categories associated with a post.

Marzio Carro

Adds categories and tags functionality for your pages.
This plugin addsthe ‘post_tag’ and the ‘category’ taxonomies, which are the names of the existing taxonomies used for tags and categories the Post type ‘page’.
This enables the categories metabox and the tags metabox in the New or Edit Page interface.
The plugin has no settings, does not alter the database and only uses hooks to 
achieve it’s goal. It works perfectly fine with Multisite installations.
This plugin WILL NOT add any display of categories or tags to your template files.
Plugin’s website: <a href="http://technotes.marziocarro.com/category/wordpress-plugins/" rel="nofollow ugc">http://technotes.marziocarro.com/category/wordpress-plugins/</a>
Author’s website: <a href="http://technotes.marziocarro.com/" rel="nofollow ugc">http://technotes.marziocarro.com/</a>

Category Tag Pages

Wonderful functionality

Yes, it works. Uses very few lines of code and it's a simple and safe solution to have categories and tags in pages.

It works

Adds categories and tags functionality for your pages.

RS Simple Category Selector vs Category Tag Pages