I have come across an excellent page on R Graphics, the R Graph Gallery. There are a few innovative visualizations, and the page demonstrates how a vibrant internet community can create a comprehensive dictionary of visualizations. Each graph comes along with the source.
Just as an example, here are two graphs with best scores (the images are clickable):
(similar to our visualizations of the US Senate)
This is really an impressive library, especially with the source of all the graphics attached.
It's a good start for your own custom graphics, although one should be cautious to see the examples as good programming examples – at least some of the few I ran across could have been solved better.
We are still waiting for such a library showing how one should use graphics for data analysis properly!