This is a graph showing the dependencies between the packages that come with GHC. I just added some (trivial) support to the ghc-pkg tool to generate the output in dot format, and generated the above graph with
ghc-pkg dot | tred | dot -Tsvg >pkgs.svg
Note the “tred” filter, which eliminates clutter from transitive edges. The ‘ghc-pkg dot’ command should be in GHC 6.12.1.