A screencast or PDF showing unique techniques and patterns used by Rubyists.
Dave Thomas' series is good on this topic.
Ahmed Al Hafoudh commented
The core of ruby programming is to use common patterns and techniques. Screencast would be very nice!
There are few resources that provide guidance on idiomatic Ruby programming. Thus there is oppty for a focused PDF/screencast that provides an overview of the subject. This could list key idioms & provide descriptions/examples of use (within a small sample application). This would be appealing to beginning and intermediate Ruby programmers --esp. those coming from other languages.