Here is a collection of articles I have found useful for various WordPress development issues.
I will add to the list over time to be sure to bookmark the post.
(Last Edited 01/04/12)
Getting custom menus into your theme – A nice introductory article by the guys at Think Vitamin.
Adding sub-page information into a parent page – This handy little code sippet comes straight from the Codex and allows you to add child page information into the layout for your parent page.
Customise the WordPress Admin Area – A guide on customising the WordPress Admin Area, useful when removing things useless to the client you are developing for.
Useful WordPress Themes, Tools and Plugins – A really big list from Smashing Magazine with links to various WordPress related content.
5 Ways to including templates in WordPress – A nice quick rundown of ways you can include template files.
Cheers to Paul for proving some of the links.