Stripe is a payment processing API built for developers. Their API is a wonderful example of a clean and understandable API, with very good documentation.
I've been heavily using Stripe's API for a project recently, and noticed that not only is the documentation well done, but the examples are presented using my own data! What a brilliant move! When I look at the official documentation of a particular API call, the example request and response JSON is shown using my email, my address, the charge amount I'm using, my metadata. It's so much easier to read the documentation when it's data that I inherently know and understand.
Thanks Stripe for raising the bar again.