I’ve written about Sankey diagrams before. Here’s a novel use: InfluenceMap has used a Sankey diagram to demonstrate “How much big oil spends on obstructive climate lobbying”. The figure that’s available for media is shown below.
InfluenceMap also offers a spreadsheet of supporting online material.
By the way, Sankey diagrams can applied to other purposes, as Sergey Bryl’ shows for shopping cart analysis with R. There is also a package, riverplot, which is intended to be devoted to this kind of plotting, but it has not been updated for the latest R release.