Cocoa Programming for Mac OS X (3rd Edition) by Aaron Hillegrass
iPhone Developers's Cook book by Erica Sadun
Programming in Objective-C, by Stephen Kochan, teaches the fundamentals you’ll need to get your work done.
Learn Objective-C on the Macintosh, By Mark Dalrymple and Scott Knaster.
Applescript Handbook by Danny Goodman
iPhone Open Application Development by Jonathon Zdziarski
XCode 3 Unleashed