A few links to some RubyCocoa tutorials I found helpful in addition to the ones you can find on this weblog:
This is a wonderful tutorial that both teaches you some basic GUI programming with RubyCocoa while teaching you a testing approach. I don’t recommend it for complete beginners, however.
Create nice selectable toolbar items for your prefs window. Two part tutorial.
Shows you how to create an application that speaks a line you enter. Lots of comments in the code makes this one nice. Uses an example from Hillegass book.
A lot of people have mentioned this around the net but this is over a year old and I had trouble getting things to work in my newer XCode environment.
Shows you how to use views housed in separate nibs. Just provides you with some code without much explanation.
I recently translated these tutorials from Japanese.
A much longer list of tutorials can be found here.