As wxWidgets development gathers speed more new features are appearing. These look like add-ins that will become part of the core toolkit.
First up there is wxAUI (wxWidgets Advanced User Interface) which provides a really nice and simple docking toolkit. It has great looking hint boxes for docking and the ability to use transparency for drag effects. It also has a notebook style tabbed interface built into it, and provides toolbar docking which is really top notch. This is now part of the main 2.7 development distribution.
wxFlatNoteBook is a tabbed "notebook" interface much like what you see in Visual Studio (or indeed Code::Blocks which uses it). It has lots of professional looking rendering and custom drawn styles.
wxFlatMenu has just been released on the wxWidgets forums. This provides custom drawn menus much like what you see in Windows XP applications like Office and Visual Studio (both 2003/2005 and 2007 look).
wxFlatNoteBook and wxFlatMenu have not been put into the main trunk, but there are plans afoot to integrate both into the wxAUI interface. With this collection of very decent extensions it opens up wxWidgets to more possibilities.