Calculus of Variations and Optimal Control Theory: A Concise Introduction, by Daniel Liberzon.
Lecture notes by Hector Sussmann
300 years of optimal control, a historical article by Hector Sussmann and Jan Willems
Feynman's lecture on the principle of least action
Article by McShane
Article by Bliss
Lecture notes by Alberto Bressan (scroll to the bottom of the page)
Tutorial on viscosity solutions of HJB equation by Alberto Bressan
Contributions to the theory of optimal control, 1960 paper by Kalman
An introduction to the coordinate-free maximum principle, paper by Hector Sussmann about maximum principle on manifolds
Lecture notes by Lawrence Evans
Lecture notes by Andrei Agrachev
Optimal Control Theory, by Emanuel Todoro
Optimality conditions for nonlinear optimization, slides by Yinyu Ye.
Noncooperative Differential Games: A Tutorial by Alberto Bressa.