QGIS does not create a proper legend for maps with pie charts or circles with variable size. I wrote a program to produce legends in Scalable Vector Format (SVG). In the QGIS Composer, the result can be added to the map as an image. If necessary, the legend can first be modified with a SVG-editor like Inkscape.
Download the program here:
LegendSVG (Windows)
LegendSVG (Linux)
Met de nieuwste versie (29 april 2012) kan nu ook een legenda worden gemaakt voor een kaart met staafdiagrammen.
Dear Sake,
could you tell me, how to do that, please?
Take care, Mario
This article describes how to create a map with bar charts and a legend:
http://www.qgis.nl/2012/05/02/staafdiagrammen/?lang=en