I wish Anguish, Buck, and Yacktman would update their Cocoa Programming book. I found that to be the perfect compliment to Hillegass' book, well-written and going into great detail (1200+ pages) about the workings of Cocoa. It had a lot of stuff that Hillegass omitted such as multithreading in Cocoa, networking (Hillegass does have some of this in the most recent versions), distributed applications, optimization, advanced Quartz drawing, and much more. Unfortunately it is now almost hopelessly out of date, being written pre-Panther IIRC. No bindings, no Core Data, no Core Animation, nothing about XML, etc.. Yacktman and Buck are writing a Cocoa design patterns book for 2009, hopefully they'll have time and desire to update this book. I imagine the potential market for Cocoa books is significantly larger than it was in 2002.
EDIT: Added Buck.