Official source for the classic Doom game ported to the iPhone.

A small cocoa framework for resurrecting an object graph, specifically designed with a view controller structure on the iPhone.

Plausible Blocks (PLBlocks) provides a drop-in runtime and toolchain for using blocks in iPhone 2.2+ and Mac OS X 10.5 applications. Both the runtime and compiler patches are direct backports from Apple's Snow Leopard source releases.

UIView graphing class.

The Oolong Engine is written in C++ with some help from Objective-C. It will help you to create new games and port existing games to the iPhone and the iPod touch. Here is its feature list:

OpenGL ES 1.1 and OpenGL 2.0 (only on iPhone 3GS) support
Math library that supports floating-point calculations with an interface very similar to the D3D math library
Support for numerous texture formats including the PowerVR 2-bit, 4-bit and normal map compression formats
Support for PowerVR's POD (Scene and Meshes), .3DS and .blend file formats
Touch screen support
Accelerometer support
Text rendering to support a basic UI
Timing: several functions that can replace rdstc, QueryPerformance etc.
Profiler: industry proven in-game profiler
Resources streaming system
Bullet SDK support (for 3D Physics)
Audio engine with OpenAL support
Networking with the ENet library

Code samples open sourced from the book iPhone SDK Programming: Developing Mobile Applications for Apple iPhone and iPod touch, by Maher Ali