What benefits for the developer does the Ruby language have that are not available in C# (preferably with code examples)?
Check this articles: What Is So Great About Ruby?, also don't miss Poor Man's Singleton Methods via Dynamic Wrappers in C# as answer to first article.
Ruby's extremely dynamic nature makes it very easy to create Domain Specific Languages. Ruby on Rails is the ne plus ultra of this aspect of Ruby as far as I know. RoR's ActiveMigrations is a DSL that takes a very difficult problem set and addresses it in a way that is easy to understand and to use. ActiveRecord, too.