Ever wondered how to build your own Wordpress plugin? Devlounge is half way through a comprehensive guide on doing just that! Check it out!
http://www.devlounge.net/articles/php/how-to-write-a-wordpress-plugin-introduction
http://www.devlounge.net/articles/php/seven-reasons-to-write-a-wordpress-plugin
http://www.devlounge.net/articles/php/how-to-get-ideas-for-wordpress-plugins
http://www.devlounge.net/articles/php/structure-of-a-wordpress-plugin
http://www.devlounge.net/articles/php/wordpress-plugin-actions
http://www.devlounge.net/articles/php/wordpress-plugin-filters