The folks at Information is Beautiful have assembled a nice dataset consisting of measurements of the effectiveness and popularity of 129 different dietary supplements. The graph they produced is appropriately beautiful and interactive, although I don't find it particularly useful for addressing the main question -- is there some relationship between effectiveness and popularity? That is, are people using the useful supplements or are they just popping snake oil?
I downloaded their data and produced the following scatterplot. I've highlighted some of the key outliers.
(h/t Harris Masket)