Below are lecture notes from classes I have taught in the past. They are free for anyone to take and use. Penn State also maintains a repository of open courseware.
Graph Theory
Penn State Math 485 (Graph Theory) Lecture Notes (LaTeX Source)
US Naval Academy SA403 (Graphs and Networks) Lecture Notes (LaTeX Source)
Game Theory
Penn State Math486 (Game Theory) Lecture Notes (LaTeX Source)
US Naval Academy SA486 (Computational Game Theory) Lecture Notes (LaTeX Source)
Optimization (Linear and Nonlinear Programming)
Penn State Math 484 (Linear Programming) Lecture Notes (LaTeX Source)
Introduction to KKT Conditions (LaTeX Source)
Penn State Math555 (Numerical Optimization) Lecture Notes (LaTeX Source)
US Naval Academy SA 486 (Introduction to Machine Learning through Optimization) Lecture Notes (LaTeX Source)
Ordinary and Partial Differential Equations
Penn State Math 251H (Honours Ordinary and Partial Differential Equations) Lecture Notes (LaTeX Source)
Penn State Math 412 (Partial Differential Equations) Lecture Notes (LaTeX Source)
US Naval Academy SA367 (Intro. to Modelling) Lecture Notes (LaTeX Source)
Linear Algebra
US Naval Academy SM361 (Intermediate Linear Algebra) Lecture Notes (LaTeX Source)