A combination of IrfanView and MS Paint. Paint is better for moving things around but is limited in line widths and rotation angles.
IrfanView also has a screen capture which works pretty well.
I'd like to make a few gifs with the arrows in motion but never get around to it. That would better convey the idea of the electricty flowing.
Of course the guys who remember their electric studies will then point out that the electrons flow the other way. LOL.
