What are all the best online (i.e. free) resources on API design?

What are the best (i.e. most elegant) APIs to study?

P.S. my goal here is to have a thread that complements this previous thread asking about the best books on API design: http://news.ycombinator.com/item?id=1668561

Here are the recommendations from that previous thread:

Online Resources:

-- "The Little Manual of API Design" by Jasmin Blanchette http://chaos.troll.no/~shausman/api-design/api-design.pdf

-- GoogleTechTalk "How To Design A Good API and Why it Matters" by Joshua Bloch http://www.youtube.com/watch?v=aAb7hSCtvGw (video) http://lcsd05.cs.tamu.edu/slides/keynote.pdf (slides)

-- "Designing Qt-Style C++ APIs" by Matthias Ettrich http://doc.trolltech.com/qq/qq13-apis.html

-- "Practical API Design" site http://wiki.apidesign.org/wiki/Main_Page

Books:

-- "Practical API Design" by Jaroslav Tulach http://amzn.com/1430209739

-- "Interface-Oriented Design" by Ken Pugh - http://pragprog.com/titles/kpiod/interface-oriented-design

-- "Service-oriented design with Ruby on Rails" by Paul Dix http://amzn.com/0321659368

-- "C Interfaces and Implementations" http://sites.google.com/site/cinterfacesimplementations/ http://amzn.com/0201498413