What are the best sources to learn Advanced Wordpress, Joomla, Drupal, and VBulletin?

Hello Everyone,

I want to be master of all 4 Wordpress, Joomla, Drupal, and VBulletin. I want to learn wordpress in such a way that I can create my own themes and plugins. Similarly I want to master Joomla, Drupal and VBulletin also. Please show me some sources where I can get free tutorials to learn all 4 CMSs and work like an expert in all 4.

Thank You

then visit forums that deals on this subject and learn form experts right there

Drupal developers are getting high salaries in this current boom, you can focus on drupal platform.