One important component of a teaching portfolio is a statement of teaching philosophy, with some good resources available from the teaching & learning center at Iowa State.
Allison Boye (Texas Tech University) has created a white paper that condenses a number of good points about developing a statement of teaching philosophy.
A May 2009 special report from Faculty Focus contains nearly a dozen short (one or two pages) essays on different aspects of creating a philosophy of teaching statement.
The Center for Research on Learning and Teaching at the University of Michigan has assembled some resources on developing a teaching philosophy, including examples from a variety of disciplines and a rubric for evaluating such statements.
The Center for Teaching and Learning at the University of Minnesota has created a step-by-step process for developing a teaching philosophy.