rfcgraph is a simple Python script that uses Graphviz to generate a very large graph showing the relationships between RFCs. Here's a small version of the graph:
The full version is in PDF format with clickable nodes, and is available here: http://static.quadpoint.org/rfcgraph/rfcs.pdf
The source code used to generate the graph can be obtained via git:
git clone git://github.com/msparks/rfcgraph.git
You can also view the project on github.
To run rfcgraph, you'll need to get a copy of the RFC index XML file (rfc-index.xml) from rfc-editor.org. Then run:
./rfcgraph.py -h
to see the usage.
Note that rfcgraph and graphviz are very memory intensive. On the order of 2-2.5GB of RAM is needed to generate the full graph.