Christos Papadimitriou and Kenneth Steiglitz, Combinatorial Optimization, Dover. This can be bought in the bookstore. We will not use very much of the book for this course but it is a very good book, so you may want to buy it anyway as it is cheap.
Alexander Schrijver, A course in Combinatorial Optimization, notes from CWI, January 2009. Available from the course page for download (with permission from A. Schrijver).
Samir Khuller, Design and analysis of Algorithms: Course notes. Available from the course page (with permission from S. khuller).
Jørgen Bang-Jensen og Gregory Gutin, Digraphs: Theory, Algorithms and Applications, Springer Verlag 2001. Available for free download from this page.