Sankey Diagrams are useful for showing flows, such as energy flows or movements of people. My favourite example is the Energy Flow Chart, produced annually by the UK's Department of Energy and Climate Change.
National Archives. It's interesting to see the shift from coal to gas and the reduction in energy consumption by industry over this period. Note that different units are used in the 1974 and 2012 charts; 1 toe equals approximately 397 therms (DUKES 2013 page 229).
DUKES Annex H includes detailed flow charts for individual fuels.
There's an entire blog on Sankey diagrams at sankey-diagrams.com, which is useful for inspiration and for advice on design. The site includes a list of software for creating the diagrams.