A very neat command I learned about today is the watch command. This command line program executes a command periodically and shows the output in full screen. If you've ever used the top command, it's the same concept, but you can use any command.
For example, the command sudo watch cat /proc/meminfo will display the current memory information, updating it every two seconds by default, until the ctrl + c combination is pressed.
I learned about this command while setting up software raid in Linux (more on that later) as it was used to watch the progress of the creation of the raid volume.