For my introductory philosophy courses, such as 'Great Philosophers' this semester, I always teach Descartes' Meditations. However, for my 'Fundamental Questions' course I've been using The Good Life, edited by Charles Guignon, and he includes selections from The Passions of the Soul rather than the Meditations or the Discourse on Method. Which means that rather than concluding with the problem of Cartesian dualism I was beginning my lectures with his attempted resolution.
Discussing this material reminded me that I had wanted last year to read The Correspondence Between Princess Elisabeth of Bohemia and René Descartes, edited by Lisa Shapiro (University of Chicago Press, 2007; it is part of their series "The Other Voice in Early Modern Europe"), as a companion to Descartes' published work. This month, I finally did, and it was well worth the effort-- not the effort of reading their correspondence, but of fitting it into the reading stack. They prove to be a lively and engaging pair. Elisabeth refuses to accept Descartes' attempts to dodge her objections to his dualism, and he proves willing enough to eventually draft an early version The Passions of the Soul to answer her questions, only to, of course, provoke more objections and questions. Elisabeth, for her part, seems to approve of the Cartesian perspective in general, although she seeks to overcome the dualism between mind an body, and to work out (with Descartes) an ethics that can help her with both personal and political situations. Along the way, they discuss Seneca, Epicurus, and Machiavelli. If not for anything else, there are unlikely moments for those accustomed to Descartes' published work, such as his admission that "the Schools are right to say that the virtues are habits," or his verdict on Machiavelli: after noting the faults of The Prince, he notes that "I have since read his discourses on Titus Livy where I noticed nothing evil."
I can't always say that I like reading the winding paths of philosophers' correspondence. That being said, I recommend The Correspondence Between Princess Elisabeth of Bohemia and René Descartes to the reader who is looking for a different and not often noticed side of early modern philosophy and letters.