My favorite icon is the UZMO lightbulb. I draw it many times in my trainings and of course I am biased, as I work very close with Martin Haussmann, who author of the “UZMO – Thinking with your pen” book.
The reason I love this icon is multi-facetted. By no m eans is this lightbulb the prettiest lightbulb-icon. I helps people understand though, how easy it can be to draw an icon and how easy it can be to remember how to draw an icon.
It is also a great teaching icon, as order, line-closure and proportions are so important. I have seen many examples where the lightbulb resembles a crying baby.
Once the drawing of the lightbulb has been mastered, the shine effect can add another layer of complexity, which again, is a great teaching object.
So overall, the UZMO lightbulb has got more to tell, than what it looks like :)