Some things that may help...
Irrlicht engine
A very fast 3D engine that also can be used to make GUI's very easy to use, also has support for images, models, quake maps, sound \ music and a number of other things including some physics engines.
GTKMM
A C++ interface for the GTK+ library used to make GUI's.
DevPaks.org
A number of good librarys
Open Scene Graph
A very very nice looking 3D game \ graphics engine :P
Hope this helps
