For a book I just published on data graphs for legal managers, available on LeanPub, I compiled as many extension packages and functions as I could locate (on CRAN and github). Here is a link: https://www.dropbox.com/s/ku2gyvlvvq1cyfa/ggExtensions.pdf?dl=0 to a pdf of the results.
If you know of any that I have missed, I would much appreciate hearing from you with a comment. Thank you.
PS If anyone would want to join me in preparing examples of the extensions or functions, somewhat like a CRAN Task View but with vignettes, that might be edifying.