Toastify is a great little app that allows you to add hot-keys to Spotify. If you haven't already heard of Spotify, it is a streaming player that allows you to listen to music for free.
I've been looking for a way to add hot-keys to Spotify for ages, and came across this slick application. It's written in C# and WPF.
From the site:
Toastify adds some missing functionallity to the Spotify client (Windows only). It shows a popup, toast style, dialog on track change and it allows you to use global hot keys for Play/Pause, Next, Previous etc.
It is fully configurable and uses an XML file to set the hot-keys. Although the keys that it comes with by default are pretty handy.
Download the app at the following link.