Firs of all: After ten years working with content management systems like Mambo, Joomla, Typo3, Fiona I started to learn Drupal 7 last year.
My opinion: Drupal 7 is great. At the moment I don't wanna work with different cms. It is scalable, customizable, responsive - if you want e.g. the open framework from the stanford university, modular, very fast and after all readable.
I don't wanna forget to mention drush, the swiss knife for Drupal.
Ok, enough advertising. Back to your question:
A good start for free is 4 weeks of drupal:
The best I've ever seen is stuff from build a module:
HTH! Good start, Ingo