What are some good resources for winforms development?
For example, when you have to have a bunch of different controls and event handlers on one form. Do you use partial classes, user controls, special attributes,...?
How do you handle communication between user controls - only with events?
Are there any patterns you can use?
http://windowsclient.net/ is a good start. When we do winform development at work we use a MVP type of pattern and try and minimize the code behind. For user controls to communicate you can do events or implement a mediator pattern.
Since you are looking for design techniques for your forms inner architecture, you may find "The humble dialog box" from Michael Feathers helpful. Not specific for WinForms, of course, but a general suggestion how to separate the logic from the layout to make your code better testable.
If you are looking for a WinForms book, there is the book from Charles Petzold. It is a little bit outdated (still .NET 1.1, AFAIK), but I don't know any better book about WinForms.