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Here are some sites that specialize in Ruby and/or Rails screencasts. Some are free and some are commercial.
Screencasts have a number of disadvantages over books or web resources. Screencasts are a rather passive medium and they go at their own pace. It's hard to put bookmarks into screencasts, add your own notes, etc. And they're not very good at going through a wide set of possible alternatives.
It's useful to keep in mind that the information density for a screencast is a lot less than for a book. Given the video and audio it may seem richer, but most of the video is relatively static, and word-for-word you've got more in a book, even a short PDF eBook.
Where screencasts can be helpful is when they take you through a long process that is composed of a relatively fixed set of steps. And they can give you a better sense of how long certain processes take.
Why are there so many screencasts out there? Well, they're relatively inexpensive to produce, and “consumers” have lower expectations of them. And some people seem to think they will be easier than reading a book.
We suggest you pick an issue you'd like to explore or a problem you'd like to solve, and first try using a screencast to address the issue, and follow that up with an appropriate book or other text resource. You'll be in a good position to create your own list of advantages and disadvantages of each.
Railscasts offers over one hundred free screencasts with high production values.
Rails Plus is quickly approaching the 100 mark.
PeepCode has a wide variety of screencasts that they sell for $9 a piece. There are discounts if you buy in larger quantities.
The Pragmatic Programmers
The Pragmatic Programmers are latecomers to the screencast scene, only having four to offer in the spring of 2008. They divide their screencasts into “episodes”, each one is about $5 for about one-half hour.