Here's a site that I really like.
The Avraham Y. Goldratt Institute was founded in 1986 as an international
educational organization committed to improving the world in which we live
through the development and dissemination of common sense methodologies.
Today, these common sense approaches to problems and improvements, as
well as the tools used to make them possible, are available through the Theory
Of Constraints (TOC). Check it out.