Bob Martin's "Architecture, the Lost Years" http://www.youtube.com/watch?v=WpkDN78P884
Longish and (obviously) cantankerous talk about applying old-school dependency isolation techniques. Also, "Use Case Driven Design"
Ruby framework built around the concepts of the talk: https://github.com/RetroMocha/obvious
And an example app, it can literally (and easily) switch from a Rails app to a jRuby desktop app by plugging the framework: https://github.com/RetroMocha/obvious_status
Corey Haines' "Yay! Mocks!" http://www.youtube.com/watch?v=t430e6M5YAo
A shorter, non-cantankerous talk about similar ideas from the prior, but along an path that is more immediatley applicable to normal Rails applications without the 'radical' architecture changes that the above material would necessitate.