I recently came across Railscasts via Digital Media Minute (that name might sound familiar thanks to Jim's XHTML Character Entity Reference).

Ryan Bates hosts individual episodes three times a week delivering tips and tricks for Ruby on Rails. Each screencast is less than ten minutes long and requires Quicktime for viewing. (Each episode is also available in Flash via ShowMeDo). Episodes cover a wide variety of topics ranging from layouts to security issues. Each screencast walks the viewer through the material and code is written on the fly. Ryan's explanation of the topic is always clear and concise, and the subject matter is narrowly defined to leave little room for misunderstanding. Even experienced Rails developers may find useful tidbits in this collection.

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In addition to offering an RSS feed, Railscasts content is available for free via iTunes and the iTunes Store.