What options are available for the layout of directed or undirected graphs in .NET?

Question

By graph here I mean something resembling these images:

Answer 1

Just to make the list of options complete: Graphviz4Net is open-source implementation of what Coincoin has suggested in his answer.

Answer 2

Graph# is also another option. I haven't used it personally, but I've been meaning to get around to looking over it.