Recording music from computer

So my friend just hooked me onto this website that plays some pretty cool music; a lot of techno remixes of songs that have already been made, some of which actually sounds really good. The trouble is, they only allow you to listen and don't provide a link to download from. I was wondering if there was program (for mac) that allows you to record songs or sounds that are being played on your computer (in good quality). Basically copying the song into an mp3 format that i could add to my itunes. Of course, +K to anyone that helps.