From the WordPress Codex Documentation on WordPress Themes

• Theme Development
• Stepping into Template Tags
• Template Hierarchy
• The WordPress Loop
• The Loop in Action
• Query Posts Function
• Theme Development Checklist
• Theme Review
• Theme Unit Test
• Using Custom Fields
• Widgetizing Themes
• Conditional Tags
• Designing Themes For Public Release

WordPress Theme Checklists

• Tutorial – Checklist for Building a Website with WordPress
• WordPress Theme Development Check List – PDF Version – WP TOY
• 15 Things You Must Do Before Changing WordPress Themes – WPBeginner
• WordPress Theme Development Checklist Tool – WPLover
• 10 Checks to the Perfect WordPress theme – Yoast

Customizing a WordPress Theme

• Cleaner Titles in WordPress – Konstantin Kovshenin
• Elegant and WordPress Designs – Best Practices – Noupe
• Theme Review: Digging Into Twenty Eleven
• WordPress Theme Hacks – WebDesignerWall
• WordPress Cheat Sheets: Theme Anatomy Model
• Collection of WordPress Hacks
• How to create your first website in 7 simple steps using WordPress
• Build A Dynamic Design Portfolio with WordPress – Darren Hoyt Dot Com
• 10 useful WordPress theme hacks – Designer Daily
• Mastering Your WordPress Theme Hacks and Techniques – Noupe
• WordPress Theme Hacks
• Handy WordPress Hacks And Tricks for Developers – Webgranth
• Add custom parameters into the body_class() function – WPRecipes
• WordPress Editor Style – Write a (CSS) Stylesheet – Yoast
• WordPress Theme – The Anatomy, an Infographic – Yoast
• Optional Styles in WordPress – Yoast
• How to add your own meta copyright to your WordPress blog – WPRecipes
• How to easily disable theme changing – WPRecipes

The WordPress Loop

• The WordPress Loop – CSS-Tricks
• 4 Ways to Loop with WordPress – Digging into WordPress
• 3 Ways to Reset the WordPress Loop – Digging into WordPress
• Easily Adaptable WordPress Loop Templates: Basic Loops, Mullet Loops, and More – Perishable Press
• WordPress Loop – Ptah Dunbar
• Global Variables and the WordPress Loop – Weblog Tools Collection
• Define Your Own WordPress Loop Using WP_Query – Weblog Tools Collection
• 10 Useful WordPress Loop Hacks – Smashing WordPress
• WordPress Cheat Sheet: The Loop Code Snippet
• WordPress Cheat Sheets: The Loop Visual Model – Wptuts+
• Advanced Guide to WordPress Queries
• A Beginner’s Guide to the WordPress Loop – Wptuts+
• WordPress Custom Post Types Get Into The Loop – WordPress, Types, Post, Plugin, Custom, Themes – WP Engineer
• Rockin’ out WordPress custom loops — kristarella.com
• The WordPress Loop And Adding Content Outside Of It
• The Ultimate Guide to the WordPress Loop – Theme Lab
• Get how many posts are returned by a custom loop – WPRecipes
• WordPress: How to get custom fields outside the loop

WordPress Theme Template Files

• WordPress template part: a powerful tool
• WordPress Cheat Sheets: Template Hierarchy Map
• WordPress Template Hierarchy Diagram – WPCandy

WordPress Navigation

• Good Navigation Links « WordPress Codex
• Navigation Menus « WordPress Codex
• Replace WordPress Navigation Menu “Text Links” with Clickable Image Sprites
• Hide Pages From WordPress Navigation Bars – Welcome To WordPress
• Top 5 WordPress Navigation Menu Tutorials
• 50+ Nice Clean CSS Tab-Based Navigation Scripts
• Using Sliding Doors With WordPress Navigation by Organized Themes
• Solostream Themes and WordPress 3.0 Menu Management Function – Solostream
• WordPress: How to Use Pages in a Horizontal Navigation bar – Tammy Hart Designs
• Simple Section Navigation – WordPress Plugin – Oomph
• jQuery Dropdown Navigation in WordPress – TutToaster
• WordPress Navigation – How to Use Sort Order for scalable page navigation
• WordPress Page Navigation – Context Sensitive
• Exclude Pages In WordPress Navigation Menu – Website Magazine
• WordPress Navigation- Dropdown Menu Image – WorldOWeb
• How to Add Custom Navigation Menus in WordPress 3.0 Themes – WPBeginner
• How to Style WordPress Navigation Menus – WPBeginner
• Automatically prefetch next pages on your WordPress blog – WPRecipes
• rel=”next” & rel=”prev” for paginated archives – Yoast
• How to automatically add a search field to your navigation menu – WPRecipes

Resources and References for Developing WordPress Themes

• Easier Theme Development with Sample WordPress Content – WPCandy
• Designing a WordPress Theme – Building a Post Sandbox
• Develop WordPress Themes Offline
• Instant WordPress (Virtual Personal Webserver for WordPress installed on your computer – Windows only)
• DesktopServer – ServerPress.com (Mac and Windows Virtual Personal Webserver – Free and Paid version)
• MAMP: Mac, Apache, MySQL, PHP (Virtual Personal Webserver for Mac – free and pro)
• WAMP Server: PHP 5 Apache MySQL (Virtual Personal Webserver for Windows – Free)

Designing a WordPress Theme from Scratch

• How to Create a WordPress Theme from Scratch – Nettuts+
• How To Create WordPress Themes From Scratch Part 1 » Themetation
• The WordPress Developer Toolkit – iThemes

Developing WordPress Themes for the Public

• Building WordPress Themes You Can Sell
• Theming for the Masses Video with Michael Fields
• 6 Essential Plugins For WordPress Theme Developers – Theme.fm
• 5 Tips to WordPress Theme Developers
• Separating Frontend and Admin Code in WordPress Theme

WordPress Comments and Interactivity

• Unreplied Comments in WordPress – Kovshenin
• Display the Number of Comments Held for Moderation
• 9 WordPress Hacks to Encourage User Interactivity – Vandelay Design Blog
• 10 Handy WordPress Comments Hacks – Smashing WordPress
• How to Separate Comments and Trackbacks in WordPress
• 30 Most Wanted WordPress Comments Page Hacks – Tutorials – instantShift
• How to Separate WordPress Comments and Trackbacks

WordPress Code Hacks, Snippets, and Customization Tips

• Removing the Shortcode Video Embed from WordPress – Konstantin Kovshenin
• How to Make a Featured Post Carousel for WordPress – Nettuts+
• Hack Together a User Contributed Link Feed with WordPress Comments – Nettuts+
• How To: Style Your WordPress Gallery – Theme.fm
• How to: Customize the WordPress Tag Cloud Widget – Theme.fm
• How To: Create An Authors List Shortcode in WordPress
• WordPress Tricks: Different Colors in Different Menu Items – Theme.fm
• 5 Useful MySQL Queries for WordPress
• Theme.fm Experiments: Macros in WordPress
• Custom Fields Hacks For WordPress – Smashing WordPress
• Beginner’s Guide: How to utilize Google resources in WordPress – WPCandy
• How to make a random post button – WordPress Guy
• XML Sitemap PHP Script – Create an XML Sitemap for any filetype
• 63 WordPress Hacks

WordPress Custom Post Types

• Post Types « WordPress Codex
• Power User Tip: Custom Post Type Feeds & Google
• Custom Post Type Snippets to make you smile
• WordPress Codex – Custom Post Types
• Conditional checks for custom post types – DevPress
• Custom columns for custom post types – DevPress
• Showing custom post types on your home/blog page – Justin Tadlock
• Custom post types in WordPress – Justin Tadlock
• Custom Post Types in WordPress 3.0 – Konstantin Kovshenin
• Extending Custom Post Types in WordPress 3.0 – Konstantin Kovshenin
• Rock-Solid WordPress 3.0 Themes using Custom Post Types – Net.Tutsplus
• WordPress Custom Post Types Guide – Six Revisions
• WordPress Custom Post Type Code Generator – Themergency
• Create your first WordPress Custom Post Type – Think Vitamin
• Creating a Tabbed Widget for Custom Post Types – TutsPlus
• Using Custom Post Types to Create a Killer Portfolio – TutsPlus
• WordPress Custom Post Types Get Into The Loop – WordPress, Types, Post, Plugin, Custom, Themes – WP Engineer
• WordPress Portfolio Tutorial (Custom Post Types) Ash Blue Web Design
• WordPress Custom Post Types Customization : Create a Portfolio – Benzing
• How to create a side blog with WordPress 3.0 – Cats Who Code
• Tutorial: WordPress 3.0 Custom Post Types – Design Juices
• How To Make Your Own Events Listing Using Custom Post Types – Make Use Of
• Create a WordPress custom post type – Net Magazine
• Tutorial – Custom Post Types for WordPress – Noel Tock
• Create A Professional Portfolio Using Custom Post Types – Voosh Themes
• Create A Professional Portfolio Using WordPress 3.0 Custom Post Types – Voosh Themes
• Create a Custom Post Types Archive Page in WordPress – WPBeginner
• How to use Custom Post Types in WordPress 3.0 – WPBeginner
• The Ultimate Guide to WordPress Custom Post Types – WP Mayor

WordPress Troubleshooting

• Troubleshooting – WordPress Codex
• Fix WordPress: Common Errors and Solutions
• How to troubleshoot WordPress “White Screen” of Death – Jared Heinrichs
• Basic WordPress TroubleShooting
• Troubleshooting WordPress: Common Fatal Error Messages and How to Fix Them: Pressography
• My WordPress Troubleshooting Methodology – WP Dude – WP Dude
• Troubleshooting WordPress Problems – Blogging Tips
• How to Troubleshoot WordPress – Problogger
• Easily remove weird characters from your WordPress database – WPRecipes
• Fix “Error establishing a database connection” with WordPress

WordPress and Typography

• Providing Typography Options in Your WordPress Themes
• WordPress › WP Google Fonts – WordPress Plugins

WordPress Collection of Theme Tips

• 17 Great WordPress Hacks You Might Need Some Day – Design Inspiration
• Collection of WordPress Snippets and Hacks – Design Reviver
• WordPress Resources: The Ultimate Collection – DivitoDesign
• 10 Tips To Make WordPress Hack-Proof. The Ultimate Guide. – GUVNR
• 100 WordPress Hacks, Tips, Tricks And Resources
• 63 Essential WordPress Hacks, Tutorials, Help Files and Cheats
• 60 Most Wanted WordPress Hacks – Stylish Web Designer
• 300+ Essential WordPress Hacks, Tools and Frameworks that Will Change the Way You Develop Themes – Webitect
• 10 Useful RSS-Tricks and Hacks For WordPress – Smashing WordPress
• 10 Killer WordPress Hacks – Smashing WordPress
• 15 Useful Twitter Hacks and Plugins For WordPress
• Power Tips For WordPress Template Developers
• 5 Useful And Creative Ways To Use WordPress Widgets
• Huge Compilation of WordPress Code
• Collection of WordPress Hacks
• The Ultimate Guide to WordPress Hacks & Customizations
• 10 WordPress Hacks to Make your Life Easy – Blog Oh Blog
• 10 WordPress Hacks to Make your Life even Easier – Blog Oh Blog
• Top WordPress hacks of 2009 – CatsWhoCode.com
• Top WordPress hacks of early 2010 – CatsWhoCode.com
• 7 Essential WordPress Hacks Video Series – Copyblogger
• 10 Cool WordPress 2.8 Hacks and Tutorials to tinker with
• 8 Useful WordPress SQL Hacks – Greepit
• 30+ (More) Most Wanted WordPress Tips, Tricks and Hacks
• 30+ New Useful WordPress Tricks & Hacks
• 35 Tips Tricks To Manage and Handle Multi-Author Blogs
• 40+ Most Wanted WordPress Tricks and Hacks
• WordPress Error 404 Pages: Essential Tips and Tools
• 29 WordPress Tweaks to Improve Posts and Pages
• 10 Twitter Hacks For Your WordPress Blog – Tutorials – instantShift
• Most Desired WordPress Hacks: 11 Common Requests and Fixes – Noupe
• 15 Killing WordPress Tricks and Hacks – Skidzopedia
• Huge List of WordPress Codes / Hacks, Tricks
• 136 Massive WordPress Tutorial Collection
• 15 Killer Hacks for WordPress that Are Extremely Useful
• 55+ Most Wanted WordPress Tips, Tricks, and Hacks