Now that you're a Drupal expert, there are some additional topics you might find useful:

• Adding Hidden Site Design Notes - how to put design or maintenance notes on your site that only admins can see.
• Core modules - what the many core modules do.
• Contributed modules - a starter list to get you to the right modules, if you need them.
• Site recipes - collection of tricks and techniques.
• Localhost or testing environment setup
• Multi-site Installation
• Site configuration challenge: corporate brochure - many ways to get to a "Corporate Brochure" type site.
• Best practices guidelines - a guide to doing the right things.
• My favorite module or theme is outdated. What next? -- it happens!
• PHP and Javascript snippets -- useful code to use as is or adapt to your own needs.
• SQL snippets -- database stuff.
• CSS Tips, Tricks, and Techniques
• Theme developer's guide
• How to write automated tests
• The Road to Drupal Hell -- this should be required reading for anyone who wants to do something not in the core Drupal.