The defacto GUI framework for .NET is WPF and is part of the Microsoft .NET SDK. Additional Information:
What specific features are you looking for? WPF / .NET provides more functionality than direct Swing or SWT, but the RCP Eclipse / Netbeans / Spring projects provide a much more complete foundation for complex and modular graphical applications.
I don't know of any defacto frameworks for WPF, but maybe something like this would be of interest: