I use keepvid on the odd occasion
http://www.keepvid.com/
put the youtube url in the text field and click the small download link on the RH side of the text input box
DON'T click the "big download" or "play now" buttons as they are advertising links
down below you will get a list of options to download
DON'T click on the regular & premium buttons as again this will download crap, just click on the file you need from the list