Are there are any modern resources on how to develop games for Mac OS? I suppose this would include objective c, cocoa and opengl 3+.
The book Beginning Mac OS X Game Development with Cocoa looks very promising but isn't out until early next year.
Here are some resources for Unity 3d,
I'm developing a NES emulator with SDL.
Inside the Xcode IDE, you have access to a lot of material related with programming in Mac OS X, iPhone/iPad.
With Xcode 3
Help -> Developer Documentation
With Xcode 4
Help -> Documentation and API reference
A window will be open and you will can navigate along a lot of topics. For example, search a document called "OpenGL Programming Guide for Mac OS X". The documents can be viewed inside Xcode or downloaded in PDF format.
If you didn't know, you can mix code written in Objective-C and C++, even in the same file, try to rename a Objective-C file with .m extension to .mm extension. There are many games written in C++ for Mac OS X and iPhone. To make a game in C++ for Mac OS X, you can do a wrapper mixing C++ and Objective-C that deals with the OS native calls ( graphics, input, etc. ). Once this abstraction layer has been constructed, the game can be programmed entirely in C++.