Justin Etheredge from CodeThinked is writing a series about learning IronRuby. After showing how to set up IronRuby on your environment and how to run an application, he shows how to create classes, with properties and methods and how to interact with basic collections (arrays and hashes).

While it does not (yet) have the depth of Why's (poignant) guide to ruby, it certainly is a good starting point for any C# developer interested in learning Ruby.