Aaron Hillegass wrote a Cocoa programming book for developers new to Objective C back in 2001. It’s amazingly relevant and accurate today even though the second edition is much more appropriate for Xcode.
I just finished the first tutorial and I can confirm that the book is as good as everyone says. It’s very readable even by someone like me with no formal C programming classes or degree.
Anyone want a [random number generator](http://houseofwarwick.com/wp-content/uploads/2006/07/RandomApp.zip)?
Since you’re interested in writing Cocoa apps I would recommend you take a look at:
http://www.rubycocoa.com/mastering-cocoa-with-ruby
Why bother w/ C when you can run Ruby? 😉