I have been using a really interesting and funky application for my XCode development, a simple yet robust tool called Objectivity for Mac.
In a nutshell, what this app does is by defining a JSON call-back content, something you would expect returned, by either adding it to the text-editor within the app, or by pointing to a URL which would return the JSON, and it will generate the model-classes in Objective-C, for you so that you can then export to XCode, as header and implementation files. It's that simple, and it tries to find the type of each object in the return, whether it is an NSString or NSDate for example. I would definitely give it a go, as I am all for a Developer having a toolbox of useful tools to use when coding, in addition to XCode.
I will put out some more apps that I use to aid me in my coding. If you guys have any other recommendations, please drop me a comment here.