Debtree Generates a Dependency Graph for a Specified Package

Debtree generates dependency graphs for a specified package. The output is written to STDOUT and can be used as input for the command dot from the package graphviz ( a rich set of graph drawing tools ).
As root : apt-get install debtree graphviz

Usage : debtree package > out.dot              create .dot file
                 dot -T png -o out.png out.dot         create a graph ( PNG ) from a .dot file

Link : http://collab-maint.alioth.debian.org/debtree/index.html

Apt-rdepends  is another tool that can create dot graphs.