TikZ-dependency
A LaTeX library to draw all sorts of dependency trees and graphs
...It is based on PGF/TikZ and it can be used either with latex or pdflatex. It comes with a very comprehensive documentation that will get you started in 10 minutes, even without any prior knowledge of TikZ.
It also provides a lot of styling facilities, to let you personalize the look and feel of the graphs at your liking.