A paper receipt with a number that can later be verified to make sure that his or her vote was counted, and not lost or misread.
I've wondered since 2000 why we can't do this. If our entire banking system is basically electronic, held by computers all across the world, why can't we do the same with voting? Why do we continue to rely on archaic voting practices prone to error and manipulation?
This article brought the issue to mind again this morning: