Kenny's Descartes is notably good & important book. He says it is "designed to help undergraduate and graduate students in understanding Descartes' philosphy". The book concentrates on Descartes' epistemology, metaphysics & philosophy of mind. The penultimate chapter, on Matter & Motion, contains a sucinct account of Descartes' mechanism & a critique of the a priori side of his natural philosophy.
Preface
Life & works
Cartesian doubt
Cogito ergo sum
Sum res cogitans
Ideas
The idea of God
The ontological arguement
reason & intuition
matter & motion
Mind & body
Notes
For Further Reading
Index