Some Very Handy Terminal Shortcuts

Here's a handful of some really useful terminal commands that might make your life considerably easier.

Ctrl + a 
Move to the start of the command line on the terminal.

Ctrl + d
Log out from the terminal (when the command line is empty).
This can also complete the current running process (for example, when decrypting in GPG).

!abc 
Execute the last command in history beginning with abc.

tty
Prints the name of the terminal in which you are typing this command.

time
Determine the amount of time that it will take for a process to complete.

who
Determine the details of users who have logged onto the machine. 

free
Raw information about memory on the disk.