There is currently a huge offer of free icons for illustrating our mind maps (see my Free icons mindmap ).
However, it is more difficult to find a high quality icon set with an hand made appearance and over 700 items. This is what Vector Doodlekit provides, but it's not free, the current price is 29 €, about 40$.
The mindmap below includes several icons from the set. Click on the map to see it in high definition.
The strength of Vector Doodlekit is the icons simplicity, personally I use it also as a source of inspiration to train drawing visual metaphors on my notebook. Icons are available in 512x512 size as transparent PNG files and as vector graphics.