Writing a wordresss plugin is no easy task and it always demands you to understand the core functionality and indepth understanding of wordpress. I have found the tutorials listed below very interesting and you will be amazed to know with bit of understanding you can create a wordpress plugin on the fly.
Before going through the tutorials listed below, i would strongly suggest to read through the wordpress plugin writing page for a basic understanding on how plugins work.
1. Create a WordPress Plugin from Scratch
http://ditio.net/2007/08/09/how-to-create-wordpress-plugin-from-a-scratch/
2. Custom WordPress Plugin from Scratch
http://net.tutsplus.com/tutorials/wordpress/creating-a-custom-wordpress-plugin-from-scratch/
3. How to Write WordPress Plugin
http://www.notesbit.com/index.php/web-mysql/web-scripts/how-to-write-a-wordpress-plugin-sample-code/
4. How to Write a Simple WordPress Plugin
https://corpocrat.com/2009/12/27/tutorial-how-to-write-a-wordpress-plugin/
5. Structure of WordPress Plugin
http://www.devlounge.net/code/structure-of-a-wordpress-plugin
6. Tips for Writing WordPress Plugin
http://www.askapache.com/wordpress/writing-wordpress-plugins.html
7. Your First WordPress Plugin
http://markjaquith.wordpress.com/2006/03/04/wp-tutorial-your-first-wp-plugin/
8. Anatomy of WordPress Plugin
http://net.tutsplus.com/tutorials/wordpress/anatomy-of-a-wordpress-plugin/
9. Wordpress Plugin Development Short Tutorial
http://www.slideshare.net/chzigkol/wordpress-plugin-development-short-tutorial-presentation
10. Readymade Template for WordPress Plugin Writing
http://brolly.ca/blog/wordpress/brolly-template-plugin/
11. Getting Started with WordPress Plugins
http://fuelyourcoding.com/getting-started-writing-wordpress-plugins/
12. WordPress Plugin Writing Tutorial Video
This videos is really nice for beginners who are interested in wordpress plugin creation.
