The famous CIMGF (Cocoa Is My Girlfriend), still very interesting and funny, demonstrates in a concrete example what is true MVC programming thanks to Cocoa, compared with oldish OOP with .NET framework (and many other). The author also responds to programmers from Windows world, that don't seem to understand the advanced concepts behind Cocoa.
Finally he presents two great new tutorials about CoreAnimation : associate CoreAnimation with a Quartz Composer layer, and rendering QuickTime movies in a CoreAnimation OpenGL layer.