GUI system development resources? | Could someone recommend any good resources for creating Graphics User Interfaces, preferably in C/C++?


Currently my biggest influence is [3DBuzz.com](http://www.3dbuzz.com)'s [C++/OpenGL VTMs](http://www.3dbuzz.com/xcart/product.php?productid=30&cat=12&page=1) (Video Training Modules). While they are very good, they cover a large area of graphics programming, so only skim the surface of GUI programming.


This question does relate to "[How do I make a GUI?](https://stackoverflow.com/questions/7489/how-do-i-make-a-gui)", where there is also a rough outline of my current structure.


Any response would be appreciated.


**Edit:**
I've just read some of the answers and spotted that I've missed some points. I had to type the question twice as I caught the wrong button and lost it.


I missed two important points, first: This will be used cross platform including homebrew on a Sony PSP. Second: I want to create a GUI system not use an existing one.


**Edit 2:** I think some of you are missing the point, I don't what to **use** an existing GUI system I want to build one.


Qt in it's current form is not portable to the PSP, never mind the overkill of such a task.


That said I've decided to create an IM-GUI, and have started to prototype the code.