I second the recommendation of the Big Nerd Ranch guides. They are excellent for learning Objective-C and IOS.

I've been playing around with Ruby Motion for the past two days and since I am pretty experienced with Ruby already, I'm finding it helpful for learning ios concepts. However, if you don't have any experience with Ruby I would recommend just starting with Objective-C and xcode.

What I really like about it is that it allows me to do everything from the command line.

I can edit the ruby files in vim and then just run the rake task to open up the simulator to test the changes I just made.

There's a few example rubymotion apps at: https://github.com/HipByte/RubyMotionSamples

I find them really easy to follow.