List of Free code Windows Presentation Foundation MessageBox
MessageBoxEx - Extended MessageBox in WPF
This is an implementation of the original MessageBox which keeps most of the previous behavior, but also allows you to further customize it. The API is slightly different, but still easy to use. Customizing it may require a bit more code.
This project contains a message box service locator implementation implemented in C# and WPF.
WPF MessageBox is an implementation of a fully customizable MessageBox in WPF which has the exact same interface as the standard MessageBox class.
Customizing the message box is done by using styles and control templates.