1: Ctl + Alt + Backspace

Use this shortcut when X isn’t responding or a program has locked up your desktop and you can’t get anything to respond.

2: Ctrl + Alt + Delete

This is the big kahuna.

3: Alt + Tab

This handy shortcut allows you to cycle through all open windows, stopping on the window you want to have focus.

4: Ctrl + Alt + F*

This is one of those mack-daddy shortcuts you very well might need to use.

5: Alt + Arrow key

If you’re using Linux, you probably know about the pager that allows you to have multiple desktops at one time.

The following apply only to terminal (aka console) windows

6: Ctrl + a and Ctrl + e

If you are working in a text editor like Nano (from within a terminal window), you can get to the beginning of a line with Ctrl + a and the end of a line with Ctrl + e.

7: Ctrl + c

When you have a process running in a terminal window (say you’re following a process with the tail + f command), you can kill that process with the Ctrl + c combination.

8: Ctrl + z

This will zombie an application. If you have a process running in a terminal and you want the terminal back but don’t want to kill the application, you can hit Ctrl + z to send the process to the background.

9: Arrow up or Arrow down

The up or down arrow key, when in a terminal window, cycles through the history of commands you have issued in the terminal window.

10: Ctrl + r

via 10 Things from Tech Republic