There's two key things to know when downloading from Youtube ... 1. They don't want you to ... and 2. Files are an odd format (flv). Dozens of sites claim to solve this ... but with Youtube playing cat and mouse, reliability is often an issue.Listed below, examples that work online or as desktop applications ... some, more effective than offers ... but they're all free. With this many options you should find a solution.
Download & Convert (online)
http://youconvertit.com/
http://vixy.net/
http://convertyoutube.com/
http://www.filepop.com/index.aspx
Download only (online, file is flv)
http://clipnabber.com/
http://keepvid.com/
http://www.savetube.com/
http://www.splandoo.com/
http://www.viddownloader.com/
http://youtubeloader.com/
http://www.youtubecatcher.com/
Firefox Plugins
https://addons.mozilla.org/en-US/firefox/search?q=download+video&status=4
Desktop Applications (pc)
http://eurekr.com/download.html
http://www.benjaminstrahs.com/
http://www.save2pc.com/
http://www.vdownloader.es/
http://youtubedownload.altervista.org/
http://www.newrad.com/software/tubesucker/
Desktop Applications (mac)
http://tooble.tv/
http://web.mac.com/simonvrel/en/gettube/gettube.html
http://www.chimoosoft.com/products/tubetv/
http://www.scottkellam.com/os-x-software/get-tube-download-youtube-videos-and-audio-files-to-your-mac/
File conversion (online)
http://www.all2convert.com/index.html
http://media-convert.com/
Update - New sites i've not tested ...
http://tube2avi.com/
http://catchvideo.net/
http://www.convertdirect.com/
