We have chosen QT as the development framework for the GUI on the PC. It is very fast, supports multiple platforms (GNU/Linux, Windows, MacOS), and is coded in C++.
QT has excellent documentation here. The computers that we are using are running Debian GNU/Linux unstable, with QT version 4.2. The Documentation for that specific version is also available on the Trolltech website.
At the beginning, be sure not to miss the Tutorials and examples.
There are available several development environments and helper applications to make development under QT4 easier.
Kdevelop is a IDE (Integraded Development Environment) specially designed for QT and KDE.
QT-Designer is a helper application for creating GUI's.