I Found this on the excellent GroovyPost.com
Do you have a favorite YouTube song or video that you’d like to download? Certainly you wouldn’t be alone if you do, and Dirpy might be able to solve that problem for you. Dirpy is a free online service that will provide a downloadable link for nearly any YouTube video. If bit-torrents are blocked at your location or just plain sound risky, Dirpy might be a great way to find the music you are looking for. The beauty about simplicity is its ease of use being that Dirpy is a web application and requires nothing be installed and works on most internet browsers.
Find the YouTube video (or song within the video) that you want to download and then Copy the URL in the address bar.
Note that some videos such as those hosted with Vevo may not be available for download.
Click here to read the complete article at Groovy Post