wokamoto

You can choose (child) categories and see the posts belong to the chosen category with AJAX.
When the category you choose from the list box has child categories, the child categories will be shown in a new list box. 
Clicking the “Search” button, the list of posts belong to the bottom category which you choose will be displayed under the “Search” button.

Simple Category Search

You can choose (child) categories and see the posts belong to the chosen category with AJAX.

peterjharrison

This plugin makes it easy to have chain select category/custom taxonomy drop downs in your theme using Ajax.
The plugin was created as a way for me to use chain selects on a number of websites I have built over the past few 
years. As it was my first attempt at making a WordPress plugin, I thought it would be best to go back and update it to work with the latest version of WordPress and is now compatible with custom taxonomies.
Feel free to visit my website www.peterjharrison.me or contact me at 
me@peterjharrison.me
Have fun!

Simple Category Search vs Category Ajax Chain Selects