XUL for the user interface.

When the time will come, XUL will probably be my choice for defining the user interface.
XUL is a markup language specific for the description of user interface, even complex one. It's basically a mozilla tecnology, based on the gecko engine, but there are some projects wich allows XUL to be used to define language specific GUIs. For example, there are some project wich enable Java and Python programs to use XUL files to create GUI.
I'll give a try, one day.