Got a favorite Youtube video? Would you like to convert it to an .avi or .mp3, for your own personal use on your PC? Here are some online converters I find work well.
First is http://vixy.net/ . Converts to MP3, MP4, MOV, and AVI. I find it lags badly during peek periods, sometimes.
Then try http://www.flvix.com/. Converts the same formats and don't mind the bad English.
If that doesn't whip your cream, try http://zamzar.com/ . This one will take a URL or a file off your PC, and convert it to one of many different formats. Then it will email you a link you can use to download the converted file. I've just tried it and it worked well. You have to download it within 24 hours after receiving the email.