Idiomatic Ruby is an online presentation by Toby DiPasquale that goes through some of the more idiomatic features of Ruby, those that newcomers to Ruby might be confused by or overlook. It covers Modules and Mixins, Exceptions, Regular Expressions, Duck Typing, Iterators, method_missing, Continuations, Closures and Blocks, and is very concise and well put together.

If you have someone in your development team who isn't quite up to speed with Ruby yet, this presentation can help it all make sense.