Want to create your blog theme by yourself? ThemesWiki can help you! No matter what your CSM Platform is, inside you can find tutorials for most popular platforms. ThemesWiki is designed to provide you with comprehensive and free guides for designing web themes and templates on a wide range of Content Management Systems and related software.
Browsing Open Source category you can find more than 30+ different theme tutorials for WordPress, Joomla, phpBB, Drupal etc…
Main categories are: Content Management, Microsoft and .NET, Open Source, PHP/MySQL, E-Commerce but announced that more will be added.
Thanks for the link! themeswiki.org is a great site.