The best checkbox solution I've seen so far is the one used in this template (Here's a public document created by the template that you can view without logging in to Google Drive).
They have two cells in an extra sheet with a character or image of an unselected checkbox and one of a selected checkbox. Then in the cell where you want to use the checkbox, set the data validation to "Items from a list" and "Create list from range" and select the two cells with the characters/images. You then get a dropdown in that cell where you can select either option.
This doesn't provide the one click on/off toggle, but it's pretty close.
Update: I just set the document to editable by anyone. Without that you wouldn't be able to see how the selection works.