Wordpress Plug In

Wrox

Professional WordPress Plugin Development        

Packt Publishing

WordPress Plugin Development Cookbook - Third Edition: Explore the complete set of tools to craft powerful plugins that extend the world's most popular CMS

Independently published

Mastering WordPress Plugin Development: A Step-by-Step Guide

Packt Publishing

Wordpress Plugin Development Cookbook - Second Edition: Create powerful plugins to extend the world's most popular CMS

WordPress Plugins: The 672 Best Free WordPress Plugins for Developing Amazing and Profitable Websites (English Edition)

WordPress Plugins (Useful plugins to help you enhance and manage your website) (English Edition)

WPAZ.IT

WordPress Plugin: Come sceglierli e gestirli al meglio per potenziare il tuo sito (Le Guide di WPAZ.IT Vol. 3)

WordPress Plugins:Top 10 FREE Best WordPress Plugins for Your Site. (English Edition)

CreateSpace Independent Publishing Platform

Creating and Selling Wordpress Plugins          

Bart VA

Wordpress Plugins