Lazarsfeld's book ``Positivity in Algebraic geometry'' contains a wealth of important material and is masterfully written. Anyone doing algebraic geometry today will greatly benefit from being familiar with the contents of this book.

Edit: here is a blog post by Burt Totaro on the importance of this topic/book:

http://burttotaro.wordpress.com/2011/01/11/why-you-should-care-about-positivity/