Algorithms from P to Np by Bernard M. E. Moret, H.D. Shapiro
Peek Inside (Courtesy Amazon): http://www.amazon.com/gp/reader/0805380086/ref=sib_dp_pt/002-2641472-0020005#reader-link
ISBN 0805380086 Explains many fundamental graph and other algorithms. Introduces (I think) amortized complexity measures. Provides the necessary math in some introductory chapters.
More on this subject: