My question has two parts:
Does anyone have any tips or references to some documentation on the web about how to write GUI code that is easy to read, write, and
You should definitely look at Jeremy Miller's guide to rich client design. It is incomplete, but I believe he is writing a book on the subject.
Another blog you should check out is Rich Newman's. He is writing about Composite Application Block which is a MS best practice guide on how to structure rich clients.
You can also read this book which is only a very light read but gives you some good ideas.