Clip Converter

Dirpy is kind of on the fritz, slow loading and some errors, so here's another alternative to save your YouTube videos...

http://www.clipconverter.cc/

They have a nice extension for Chrome, to make it convenient.

Because videos tend to disappear, you know.

Dirpy

One of many YouTube downloaders.  Some important videos tend to disappear or get taken down, especially if of a sensitive nature.  Dirpy to the rescue.

http://www.dirpy.com/