I just found this excellent website that allows me to download and convert videos from Youtube to MP3. You can choose the quality from 160K, 192K and 320K!
Beside as a youtube to mp3 converter, it can also download Youtube videos as 3GP, FLV, MP4 and WebM.
So, what are you waiting for? If you want to know how to convert Youtube videos to MP3, just go to http://mp3conv.net/.