Since you brought up the Sankey diagrams I'll piggyback on you to mention that I spent a summer at LLNL and got to meet the team/person that produces these. I was also given the program they currently use (it's java, still have it somewhere. . .), and tasked to look into applying it to city flows. I have a couple of the results here[1] (my boxes are off in terms of size, but the flow widths should be correct). I still love those diagrams although I haven't touched them in 3 years. It's a fantastic way to visualize a ton of information. The trick is really just finding appropriate data.

[1] https://www.flickr.com/photos/23215983@N02/sets/721576342348...