iPhone API Explorer: Take A Live Journey through the iPhone's Classes
By 
Patrick Collison is a Canadian-based Irish iPhone developer who has put together an “API Explorer” for the iPhone.
Patrick’s API explorer shows an outline of the iPhone’s classes and uses Objective C’s run-time introspection to present the implemented protocols, methods, and instance variables of every loaded class. Not only that, but in many cases you can also interact with visual classes, drawing and resizing them to see how they look.
This is an awesome tool to play with if you find experimentation and a “top down” view the best way to learn. There’s nothing like jumping in at the deep-end! The source code is available to download from Patrick’s post.
