I can't belive that no one has mentioned
AE Button Plus.
This utility extends functionality of hardware keys on Windows Mobile devices. It allows you to:
* intercept almost any standard button: application buttons, WM5 SoftKeys, Volume slider, Action and even Red/Green phone buttons
* distinguish up to 4 different keypress events on each button grabbed (single, double, triple and "long" keypresses).
* remap each of the keypress events to "virtual" application button or assign them directly to one of the wide set of built-in actions.