In contrast to MFC where even Microsoft Word is pesumably someday going to end us as "an Integral part of Windows", Linux has a definite division between basic functionality and UI programming.
There are several options floating around - some purport to be "universal" (same source runs under both X amd MS-Windows) and some of which are special-purpose (like the gtk libraries for Gnome).
I do most of that stuff in Java these days, so I can't rate them, but if you look on SourceForge (
http://sourceforge.net) and FreshMeat (
http://www.freshmeat.net) you should be able to see many of them.