FusionCharts.
 
View XML for the above chart
In this example, we've shown a "Product Sale Estimation Chart". We're comparing the sale of three products - Inkjet Printers, Laser Printers and cartridges for the year 2005-2009. The data for 2005 & 2006 represents actual sales for the period and hence cannot be adjusted. However, the data for 2007, 2008 & 2009 can be dragged and adjusted. As such, they've been plotted using dashed lines.
 
You can also adjust the axis upper and lower limits using the context menu. This is particularly useful, if you want any column to assume a value that is not covered within the current y-axis range of chart.