KeepVid (free) allows you to download videos from many places (including YouTube, Flickr, TED, Vimeo and more) and then show in your classroom. It's free--you choose whether mac, PC, mobile, etc and the download. It really addresses where some schools 'block' all YouTube or there are buffering issues. I tend to use the mp4 version, but you have choices of file type too.
This blog poses some good questions in iPads and cybersafety, a major issue for schools. Still, you have to LOVE iPads for ease of use as an elegant too.