I am working with the .NET 3.5 MSChart controls and from time to time I find that I need to add custom properties to either the Series or DataPoints.
For example:
<MSChart is really the original Dundas Chart tool. Dundas has a listing of all custom attributes. Since they don't support Dundas Charts anymore, that link may die eventually. As of this date it is still valid.
The list is now maintained on MSDN at: http://msdn.microsoft.com/en-us/library/dd456764.aspx