I like Camstudio. http://camstudio.org/
Completely free and it works with a huge amount of codecs. Experiment with it a bit to find the best codec for length to size ratio you desire. And then be sure to Upload any good ones for the rest of us to watch! As a Warning... Be careful with the installer...it comes with a lot of Bloatware designed to make you click accept without reading the nonsense. You can still continue if you click Refuse or Decline on the first handful of the ones it asks. Otherwise it will download and installed a ton of stupid nonsense.