pkgdot is a Perl script for graphing dependencies between installed packages on a FreeBSD system. It fits between FreeBSD's pkg_info and AT&T's GraphViz.

I mean that literally — you put it in the middle of a pipeline, like this:

pkg_info -ar | ./ | dot -Tpng > out.png

And you get output like this: (click to make bigger)

example 1
example 2
example 3
example 4

Thanks to Dan and Dylan for providing pkg_info inputs for two of the above examples.