This isn't much of a primer, but we discussed graph algorithms extensively in our algorithms class last Fall 2009. We used this book,

Introduction to Algorithms, Third Edition by Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest and Clifford Stein

http://mitpress.mit.edu/algorithms/

and it also has accompanying youtube lectures from an MIT class.

http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-046j-introduction-to-algorithms-sma-5503-fall-2005/video-lectures/

Chapters 17, 18, and 19 dealt with shortest paths.