From Jakob Nielsen, usability guru. The user's experience should be similar to all other similar applications to minimize learning curve and maximize usability.
Mac OS X, which combines a powerful core foundation with a compelling user interface called Aqua. With advanced features and an aesthetically refined use of color, transparency, and animation.
lecture notes for the course Programming Graphical User Interfaces (PGUI). The course belongs to the curriculum of the Department of Computer Science in the University of Tampere.
a free library providing windowing and widgets for graphics APIs / engines where such functionality is not natively available, or severely lacking. The library is object orientated, written in C++, and targeted at games developers who should be spending t
Hardware accelerated 2D full featured middleware for all who want to develop commercial quality 2D games rapidly and easily. It covers all imaginable 2D game genres (DirectX)
a high-level multi-platform, thread-safe C/C++ windowing and graphics library built upon a fast, low-level graphics kernel. (new feature is FGX - dynamic GUI via XML file aka XUI file format)
C++ interface for the popular GUI library GTK+. Highlights include typesafe callbacks, widgets extensible via inheritance and a comprehensive set of widgets.
If you've done any Web or UI design, or even thought about it much, you should say, "Oh, right, I know what that is" to most of these patterns. But a few of them might be new to you, and some of the familiar ones may not be part of your usual design reper
a free user interface builder for GTK+ and GNOME interfaces designed are saved as XML, and by using the libglade library these can be loaded by applications dynamically as needed. (Glade can also generate C code)
How to create applications that look right, behave properly, and fit into the GNOME user interface as a whole, covers specific advice on making effective use of interface elements, and the philosophy and general design principles behind GNOME interface.