This will depend on what you’re looking for. But I wanted to make this FAQ entry to try and cover all bases.
Often times, they may take down a video for any reason they want; but I’m guessing it’s usually because they don’t think it’s good enough to be seen anymore.
In May 2010, their YouTube page was hacked and almost ALL videos were deleted. This included all the Boralogues, singles from Tally Hall’s Internet Show, random sketches, and music videos. They used this as an opportunity to re-upload in higher-resolution formats and organize things better, too.
At the time of writing this entry on 5/28/10, all the singles from T.H.I.S. were back up as well as the videos for Banana Man, Good Day, Greener, Dream, Two Wuv, and The Whole World And You (which did NOT get deleted during the hack). For the first time, Banana Man could be seen in 480p (hey, it’s better than what it was…). Other videos that were spared in the hack were the NYC series, AESTAVALIA, and Misfortune.
Perhaps you’re looking for videos from 2005 or before? If so, many of them were taken offline at some point and then the originals were wiped out during a hard drive crash Joe suffered… so they’ll never be seen again, most likely.
You can find a list of videos Tally Hall has had up over the years on the Tally Hallmanac:
(feel free to add to it if you see something missing!)
Also, some older videos were captured and re-uploaded by a fan over here: