Video: Martin Fowler on Software Design
I think of Fowler as a great visionare and even though he is (like me) more a Ruby than a Rails user, I recommend this talk to anyone who has heard about rails, but never got the values behind its ideas.
This is mostly because the talk is not that much about rails itself as it is about good software design in general. And if you are not familiar with the subjects of Martins work (object oriented design, refactoring, extreme programming, agile methods and database design), this will give you an inside why things like ActiveRecord or Scaffolds were created in the first place.
There are more interesting keynotes coming in the next few days, from people like Dave Thomas, David Heinemeier Hansson, Paul Graham and Why The Lucky Stiff!. For the last one, I'm not sure if Why will talk or if he will perform with his band.