Stacked bar charts are quite nice for presenting a relatively large amount of data in a compact space, but they have a major failing, in that it's difficult to compare similar values in different columns, unless the value is the bottom-most one in the bars.
As an experiment, I've played with adding some basic interactivity to try to address this. Below is an SVG chart that initially appears to be nothing out of the ordinary.
This is obviously super-basic; it might be good to do things like adjusting the Y-axis label numbering so that 0 is aligned with the selected element's baseline. However, I'm bored of this now, so I'm posting this up before I forget about it completely :-) The SVG code is currently entirely handcrafted, but now that all the basic concepts are in place, creating a graph from some datasource would be a fairly mundane exercise.
EDIT: I've just realized the SVG file has some console.log()s still in, which caused the animation not to work on Firefox 3.x - should now be fixed.