I wish all nonprofits would do this, but almost nobody does: actually tell donors where their money goes. Not in the form of a pie-chart of the entire budget, but what one donor's giving specifically made possible.
Donors of even modest gifts can track their gift to a specific single project. They get its name, the type of project, how many people it reaches, some background context and photos, and who else donated to it (most of them seem to be anonymous). Donors can even find their project on Google Maps.
Here's an example report.
I wish this wasn't noteworthy. I wish most nonprofits were doing this for their donors. That would help overcome one of the most common reasons people don't give: My gift won't make a difference. How many donors would say that if they knew they could expect reports like this?
Everyone who's not doing this (i.e., virtually everyone): Take charity:water's example. Treat all your donors with the respect that's due them. Figure out how to report what their gifts make possible!