Lovely Charts is a free web-based tool for creating flow charts, site maps, network diagrams, ... You can export your charts as JPEG or PNG files at the size you specify.

If you're sick of flow charting in Vizio (or whatever) and are feeling nostalgic for the good old days of ASCII art, ASCIIFlow can solve both your problems by letting you make text-based flow ...

The flow charts themselves are okay in terms of logic, but the rendering resolution needs improvement to prevent ugly "jaggies." The effect is literally magnified when you use the Export to PowerPoint ...