RealBasic is an excellent development tool. I don't know that it's a replacement for Cocoa, but I use it all the time when I need a quick GUI app.
As to Cocoa, you need a good book. I recommend
Cocoa Programming for Mac OS X by Aaron Hillegass. More info
here.
There are other good books as well of course, but this one is great for a programmer who wants to learn Objective C. I think there may be a second edition coming out soon with updates for XCode.