I've been looking for a good C/C++ GUI Toolkit for some time now, and have found these to be the general requirements:
I need it to be: Good looking cross-platform C++ or C that will compile w/C++, either is fine OpenGL support can be used in commercial applications without royalties (no licensing snags)
What I've used in the past and why they aren't what I need: -Win32 (not cross-platform) -FLTK (grey, flat, and visually unappealing, but otherwise excellent)
I've been looking at GTK rather closely, the only problem being that it doesn't have reliable OpenGL support as far as I can tell (some 3rd party support only?) Qt's license does not allow commercial development without a licensing fee.
By OpenGL support, I mean OpenGL views in the toolkit (embeddable).
You may want to reconsider Qt as your answer, and you are a few years behind on the license changes since Nokia acquired them -- that is no longer a concern as it is LGPL these days. And support for OpenGL is just one of many strong points in favor.