A nice compilation of webdev documentation:

http://devdocs.io

In my opinion Stripe [1] has pretty awesome looking docs for API.

[1] https://stripe.com/docs/api/php#create_charge

I agree; I love the side-by-side explanation and json, and the ability to toggle from python to ruby, etc.

Second that. I love reading Stripe documentation just because of easy it is to read and navigate.

I really like Vimeo's API documentation: http://developer.vimeo.com