1. Ideas from Ryan Bretag and Stephen Downes on the nature of Critical Thinking. In the case of Bretag, he has compiled an amazing list of all the attributes of Critical Thinking that he has found so far from various sources. Downes takes off from that with his own view of what makes up critical thinking.
2. An article by Barbara Fister, "In the Teeth of the Evidence", which comments on some of the difficulties in teaching CT to university students, "Maybe instead of teaching rigorous analysis that tests ideas to see if they break, we need to put a little more emphasis on understanding them better first. A little more empathy and lot more respect for evidence could go a long way."
3. A draft paper by Peter Elbow, (referenced in Fister's article) about The Believing Game, In this paper he posits that in addition to "The Doubting Game", which is what he calls the kind of critical thinking that is the academic norm, we also need to develop the contrasting skills of looking for what is possibly good in ideas we aren't intuitively drawn to,
4. Finally, a very interesting effort to create a (more or less) standardized test of critical thinking, which is being used by a number of US. liberal arts colleges and universities. It is called the CLA Test, which stands for Collegiate Learning Assessment. This 27 page pdf file explains the design of the test, gives examples of the question prompts, the evaluation rubrics, and samples of student responses.