Let me start off with this one for a very active national charity.
The swipe is a direct mail package that includes a 2-page letter (with involvement device), pledge/order form and envelope (front and back)
I'll try to get some more Not-For-Profit examples posted soon.
Here's the link for the free view / download:
Charity / Not-For-Profit: Full Direct Mail Package | Copy Swipe File Example | Free Download