Keep-Tube is another site that is very similar to KeepVid and lets you download YouTube videos straight from its website (i.e., there is no additional software you need to install). The website does run on Java, however, so you will need to have that installed to be able to download videos. Simply copy and paste the URL of the YouTube video you want to download into the blue bar at the top of the page and click on the Download by URL button. A Java pop-up window will appear asking you if you want to run the Java applet. Click Run to continue. Then, you will be able to choose from several different video formats in which to download the YouTube video including 3gp, flv, webm and mp4. Keep-Tube also allows you to download just the audio for the YouTube video in mp3 and aac format.
Check it out here: http://keep-tube.com/