You can download this free of charge from the iPhone Developer Program page on Apple’s website: http://developer.apple.com/.

Apple’s Own Documentation:

NOTE: These links require you to be a registered iPhone Developer, which you can do for free at: http://developer.apple.com/iphone/program/

Introduction to Cocoa Application Tutorial
I started with this tutorial, although the syntax of Objective-C is completly foriegn to me, it allowed me to get up to speed on a lot of the tools you’ll need to create a desktop or iPhone application.

Object-Oriented Programming with Objective-C
I jumped to this one next, but you might want to dig around in their documentaiton first, there are some great getting started guides.

Cocoa(R) Programming for Mac(R) OS X (3rd Edition)

Every Apple developer I’ve talked to has pointed me to this book. Unfortunately this version won’t be out until later this month, if you’re impatient I’m sure you’ll be able to google around and find the 2nd Edtion in pdf form.

That’s all for now.

Hopefully this will give you a little motivation to make that leap if you’ve been on the fence about it. Like I said before, I have no Objective-C, C, C++ experience, but I’m going to give it a shot anyway.

If you do decide to try it out leave a comment below or hit me up on Twitter. I probably won’t be able to help at first, but it would be nice to work along side some other developers just getting started as well.