Ruby Tapas is a bi-weekly screencast by Avdi Grimm on Ruby and Object-Oriented design principles. It's a subscription service, but some episodes are available for free.
One thing I've had difficulty with is remembering which episode covered which topic. To help with this I've compiled an index of episodes which is searchable by title and/or keywords (which I've gone through and assigned to most episodes). If you're a Ruby Tapas subscriber you might find this useful, otherwise I recommend becoming one if you're interested in Ruby.
To give you an idea of the type of content covered, here are some frequently occurring keywords:
The latter 3 are not literal keywords, but keyword patterns. For example, if you want to search for episodes covering instance methods of the Array class, then search for "Array#".