Jim Weirich's presentation on Dependency Injection (in ruby).
If you are a ruby newbie, read Jim's guide for Java programmers.
And the cherry on the cake: Jim's presentation on continuations.
For more continuation goodies, see Sam Ruby's explanation, RubyGarden #1, RubyGarden #2 and IDEA Programmer's one. (or Bruce Tate article)
You might also check Seaside(Smalltalk), Borges(ruby) and DarkSide(Io) implementations. (no link, just google for them).