Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
There aren't many screen-capturing apps for Ubuntu as there are for Windows and Mac OS X. Needless to say, you'll have to stick with the ones that are stable and are free of any bugs whatsoever. Here are some of the finest.
Though many of the screen-capturing applications focus on capturing the whole screen, it becomes difficult to record tutorials that are focused on explaining things on the command line. For example, if you are teaching your audience programming or shell scripting putting focus on the terminal might work but you won't get a clear picture of the window. Shelr is a free application that helps you address that problem.