Freecorder is going to be one of those programs that you use nearly everyday (if you use radio player or VoIP, of course)

It allows you to record real time audio no matter where it comes. It support streaming, so you can record podcasts, and now you can even record Skype conversations.

You can connect any kind of device as a music player or a microphone to use it as input sound device and record their sunds.

It has a very intuitive interface and it is really easy to use.