You can find a series of examples in D3's gallery that will keep you busy for hours!
In addition to the fantastic charting tools, D3 also enables a growing list of mapping capabilities. It is really exciting to see where all this is heading. D3's developers have been spending a lot of time most recently working on projections transformations. Check out these amazing interactive projection examples:
Adaptive Composite Map Projections (be sure to use chrome for the text to display correctly)
Can't wait to see what the future has in store for bringng custom map projections to life in more web map applications!