An update to Free Audio Editor doesn't change its simple mission, but the newest version is chock full of extra-helpful features. The application downloads YouTube videos, and then strips audio from those FLVs and other video files.
By entering a URL, you can strip audio from YouTube videos online. It downloads the YouTube video in FLV, then strips the audio from the FLV file. Free Audio Encoder will also strip audio from normal videos, such as those in AVI format.