John -
Tushar gave you several links to try out. If what you want is similar
to the "Built-in Custom" chart types (gotta love that oxymoron), but not
exact, keep in mind that you are not limited to that very short list of
chart types. Make a chart with all your data, then one-by-one, select a
series and assign it a different chart type (Chart Type from the Chart
menu) or to the secondary axis (Double click, then select the Axis tab).
You can get any number of custom chart types in this way, without
dealing with an addin.
- Jon