From iPhone to Mac programming

Question

I've looked through the site to make sure this isn't a duplicate. Apologies if I've missed something.

I've been doing iPhone development for about a year now, and I'm comfortable with Objective-C, Xcode and Cocoa (at least what's used on the iPhone), but programming for OS X seems much more involved.

What are some good free resources for someone like me? Most of the stuff I've seen is about learning Objective-C and Cocoa, and I really want to get into the parts of IB I'm not familiar with and anything else that's important on OS X that isn't on the iPhone.