The youtube-dl is a small command-line utility that can download videos from youtube.com too easily.
In terms of archives, from the Debian Multimedia already incorporates the youtube-dl. If it does not, download it here:)

Installation via apt
aptitude install youtube-dl

Use simple
youtube-dl Endereço_do_video_do_youtube (thus the name of the downloaded file is random)

Use advanced (in need of credentials)
youtube-dl-u USER-p PASSWORD Endereço_do_video_do_youtube

Use advanced (once assigned a name to the file)
youtube-dl-o filename Endereço_do_video_do_youtube

Help
youtube-dl - help

You leave here to take some videos to test this utility. These videos are a great concert, a great band, I was watching this month in the southwest, Faith No More:

"Evidence, all sung in Portuguese by Mike Patton"
http://www.youtube.com/watch?v=hAcvqSyCYhk

"Just a Man - Spectacular, Mike Patton comes to the public"
http://www.youtube.com/watch?v=VqVjYJsYXH0

"Easy"
http://www.youtube.com/watch?v=utCc7kj5RsA

"Mike Patton saying a stupidity in Portuguese language"
"Mike Patton calling King Kong a bearded"
"Joke"
http://www.youtube.com/watch?v=niD5hdFO0ZY

"Joke, with better quality"
"Mike Patton to say "Muito Tomântico"
http://www.youtube.com/watch?v=0zv6AoloFgg

"Music of entry, reunited"
http://www.youtube.com/watch?v=qv5bWk_EdAA

But if you want more, nothing like going to youtubas:) it is still well worth!

References
http://bitbucket.org/rg3/youtube-dl/wiki/Home