Thanks for your answers. I had a look at MudPie and modified it slightly to suit my exact needs. If you are interested have a look at the attached visualization. Open the SVG file in Safari, the tooltips on the edge labels give the reason for the dependencies.
@Stef: I would be interested to see a package blueprint of the code.
@Adrian: Thanks for your offer. I think Hapax is less useful in our case. We know the code pretty well, we are more looking at "hard" dependencies right now.
Lukas