One thing I've found particularly useful recently is the static code analyser introduced in XCode 3.2. One thing I missed when making the transition from Java was static code analysis and the wealth of tools available (PMD and FindBugs being two frequently used examples) to very quickly deflate your ego when it comes to the quality of your code.

Recently I have been asked to pick up the pieces of a couple of projects that other developers have abandoned (or been forced to abandon) and the analyser has been very helpful in indicating how big the mountain is I have to climb.

To run the analyser, hit "Build and Analyze" from the build menu. The results will show up in the Build Results menu in the normal way and will alert you to potential leaks (unreleased objects) and objects released, dereferences of null pointers, assumptions about pointer values, plenty of stuff to keep you busy! The web site for the underlying analyser is here.