wxGuide ("http://wxguide.sourceforge.net/") is a collection of guidelines for designing cross-platform applications written in C++ with the wxWindows framework. It gives ideas and advice on how an application could and should be written. wxGuide provides sample code which applies to all these guidelines. Each of these samples can be taken as a starting base for your own project.
The guidelines are far from complete, but the current guidelines and code are already stable and usable.