This video provides an excellent foundation for responsive design.

Well done--gave me a good overview of what Twitter Bootstrap is and can do. I liked showing the examples and how to use the Twitter Bootstrap site as a resource as you design. I also liked the overview of LESS.

This is not really a tutorial, it's more an overview of what responsive design is. Build a responsive website from start to finish without the use of bootstrap for a change. Just a plain css grid and start from there.