The release of a new tool for Sankey diagrams has passed almost unnoticed. Dr. Hanny J. Berchmans has developed Sankey Diagram Maker and provides it as freeware on Google Docs.
This very basic tool can be used to produce simple Sankey diagrams that have a left-to-right layout and breakouts to the bottom as the above. Data values are fed as text file (CSV format). Colors can be set individually and nice color gradient effects are possible.
I have added Sankey Diagram Maker to the software list.