Chris Roberts

This plugin makes it easy to add a sophisticated jQuery powered drop-down menu to your WordPress theme.

Mensy

Enables easy creation of drop-down menus in your WordPress theme.

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!

Mensy vs Category Ajax Chain Selects