Easy Youtube to MP3

FYI, this is a pretty nice tool. It allows very easy conversion from a youtube video to an MP3. The URL is http://www.youtube-mp3.org/.

There are also browser addons that add a button to the youtube page itself so that the tool is even easier to use.

Firefox Youtube to MP3 addon

Just do a search on your own for other browser addons. I haven't tried them out and I don't want to recommend anything potentially dangerous.