Writing a plugin http://codex.wordpress.org/Writing_a_Plugin
The plugin API http://codex.wordpress.org/Plugin_API
Post Meta fields http://codex.wordpress.org/Function_Reference/post_meta_Function_Examples
Taxonomies http://codex.wordpress.org/Taxonomies
Plugin’s own tables http://codex.wordpress.org/Creating_Tables_with_Plugins
Creating Options Pages http://codex.wordpress.org/Creating_Options_Pages
Administration Menus http://codex.wordpress.org/Adding_Administration_Menus
I18n for WordPress Developers (internationalization) http://codex.wordpress.org/I18n_for_WordPress_Developers
WordPress Coding Standards http://codex.wordpress.org/WordPress_Coding_Standards
Inline Documentation Standards http://make.wordpress.org/core/handbook/inline-documentation-standards/
How To: Load Javascript With Your WordPress Plugin http://planetozh.com/blog/2008/04/how-to-load-javascript-with-your-wordpress-plugin/
How To Include CSS and JavaScript Conditionally And Only When Needed By The Posts http://beerpla.net/2010/01/13/wordpress-plugin-development-how-to-include-css-and-javascript-conditionally-and-only-when-needed-by-the-posts/
Best practice for adding JavaScript code to WordPress plugins http://www.prelovac.com/vladimir/best-practice-for-adding-javascript-code-to-wordpress-plugin