Apart from the The Laser Game Tutorial. (that I recommended in my previous answer)
There is the "The Bowling Game"
Article: Discovering Better Code
Series
A.K.A. "The Bowling Example" A guided
tour through the mind of a
Smalltalker: How to build a business
model from the ground up, factoring it
along the way. If you don't understand
how Smalltalkers think or why they
think that way, you need to read this
series.
The really nice thing about this project is that it is like being the pair-programmer of a great developer.
The author Ron Jeffries is one of tho founders of Extreme Programming and a book author.
So it is a really good resource. I wish more tutorials where written like this.