An incomplete manuscript of Rene Descartes' entitled The Search for Truth is a dialogue that makes standard Cartesian arguments for the method of doubt in pursuit of certainty, the cogito as the foundation for knowledge, and the argument that we are thinking things and not our bodies. The book is motivated by the idea that all "the items of knowledge that lie within reach of the human mind are all linked together by a bond so marvellous, and can be derived from each other by means of inferences so necessary, that their discovery does not require much skill or intelligence."

I enjoyed reading this unfinished work.  It includes some humor not as evident in Descartes' other writings on the same topics.  And there are responses to some of the arguments against his views that appeared after earlier works.  It could have made for a great text to use in intro classes if it were finished.