Where can I find a good tutorial on iPhone/Objective-C multithreading?

A simple, but complete example is Multithreading in Cocoa.

And a related Stack Overflow question is NSOperation on the iPhone.

Don't forget the official documentation from Apple: Threading Programming Guide

You will find complete explanations and example code.

• Cocoa Tutorial: NSOperation and NSOperationQueue

• Cocoa for Scientists (Part XXI): Multi-Threading Your App with NSOperation and NSOperationQueue

• Concurrent Operations Demystified

• A Guide to Threading on Leopard

Once again, if I may promote my iPhone development course, I had a class devoted to multithreading last semester, covering basic threading, locking, dealing with the UI on the main thread, and NSOperationQueues, for which the class notes can be found here. This fall semester that same class will be dominated by Grand Central Dispatch.

The video for the class can be downloaded for free from iTunes U.