I had the same question and searched for good GUI toolkits.
At the end I found out, that a GUI toolkit isn't enough - I need a complete platform independent solution providing me the build environment, IDE integration and lower level functions like network sockets and file I/O.
My result? Since nearly 9 years I use Qt (but the first years only for GUI stuff) - now I have highly complex networking apps with load balancing, massive multithreading and image processing.
You can use Qt as commercial user with professional support (like me) or just start your own projects under GPL and with 4.5 with LGPL (which allows commercial use).
The other alternatives like wxWidgets and GTK++ are very good choices for GUI programming.
But if you want a well documented and complete solution, then Qt is your choice.
Best Regards,
3DH
