Read in this order:

  1. Developing with Core Data
  2. Introduction to Core Data Programming Guide: Core Data Basics
  3. Introduction to Core Data Programming Guide: Managed Object Models
  4. Introduction to Core Data Utility Tutorial
  5. Creating a Managed Object Model with Xcode
  6. Xcode Entity Modeling Tools for Core Data
  7. Non-Standard Persistent Attribute
  8. The remainder of Intro to Core Data Programming Guide

From the iPhone Reference Library

  1. Core Data Tutorial for the iPhone OS
  2. Core Data Programming Guide

Cocoa Dev Central Articles:

  1. Core Data Class Overview
  2. Build a Core Data App