I like the Youtube logo because it is simple but represents its website perfectly.  It is nice that the red box that is used in the logo is the shape of an older, more retro television screen.  Youtube was started in February 2005 but I am unsure as to whether  or  not the founders of Youtube designed the logo or not.  Apparently the logo has undergone a few changes since the website was started in 2005, but it doesn't seem to have effected the recognition of the logo or the website that it represents. The font used for the logo is alternate gothic.

info from - http://famouslogos.net/youtube-logo/