MediaKeys is a free, small, portable program for Windows, which runs from your system tray, that allows you to set specific keys (now fully customizable) on your keyboard to control your media player globally. This works even if you haven't invested in an overpriced keyboard with built-in media keys but if you do already have one, MediaKeys offers a greater level of control and has fantastically useful extra functions. The controls available are Play/Pause, Skip to Next Track, Skip to Previous Track (the last two can be held down to rewind / fast-forward the current track).
The compatible media players are as follows; Windows Media Player, iTunes, Winamp, foobar2000, MediaMonkey. Currently, they are the only fully compatible programs but others are constantly being added (VLC is next). Also, there is a 'generic media player' option which provides limited controls for a huge number of media programs. Feel free to request full compatibility for a program (see 'Feedback / Bugs' section).
There are also a number of extra built-in controls, such as those to control the volume via keyboard and mouse and pressing your self-customized 'play' key to start your media player.
MediaKeys runs in the background from your system tray. You only need to see the settings window once to configure your controls; after this it will stay out of our way unless you invoke it with a keyboard shortcut, if you decide to change your setup. MediaKeys also has an option to run on startup either on all accounts or just your own you don't need to load it every time you switch your PC on.