First install graphviz for your OS, then
go get github.com/davecheney/graphpkg
To graph the dependencies of the net package:
graphpkg net
graphpkg can also filter out packages that do not match the supplied regex, this may improve the readability of some graphs by excluding the std library:
graphpkg -match 'launchpad.net' launchpad.net/goamz/s3
By default graphpkg shows the graph in your browser, you can choose to print the resulting svg to standard output:
graphpkg -stdout -match 'github.com' github.com/davecheney/graphpkg