Linux - Ubuntu general shortcut

General keyboard shortcuts

Ctrl+A = Select all (In Documents, Firefox, Nautilus, etc, not Terminal)
Ctrl+C = Copy (In Documents, Firefox, Nautilus, etc, not Terminal)
Ctrl+V = Paste (In Documents, Firefox, Nautilus, etc, not Terminal)

Ctrl+N = New (Create a new document, not in terminal)
Ctrl+O = Open (Open a document, not in terminal)
Ctrl+S = Save (Save the current document, not in terminal)
Ctrl+P = Print (Print the current document, not in terminal)

Ctrl+E = Send To... (Send the current document to an email recipient or remote location, not in terminal)
Ctrl+W = Close (Close the current document, not in terminal)
Ctrl+Q = Quit (Quit the application, not in terminal)

Ctrl + Alt + F1 = Switch to the first virtual terminal
Ctrl + Alt + F2(F3)(F4)(F5)(F6) = Select the different virtual terminals
Ctrl + Alt + F7 = Switch to current terminal session with X

Ctrl+Alt++ = Switch to next X resolution (Depends of your X configuration)
Ctrl+Alt+- = Switch to previous X resolution (Depends of your X configuration)

Ctrl + Alt + Backspace = Kill X server

Alt+Tab = Switch between open programs
Printscrn = Print sreen




Command line / Terminal shortcuts

Ctrl+C = Kill process (Kill the current process in terminal, also used to copy elsewhere)
Ctrl+Z = Send process to background
Ctrl+D = Log out from the current terminal. In X, this may log you out after a shuting down the emulator.

Ctrl+A = Home (Move cursor to beginning of line)
Ctrl+E = End (Move cursor to end of line)
Tab = List available commands from typed letters (Ex: type iw and click tab, output = iwconfig iwevent iwgetid iwlist iwpriv iwspy)

Ctrl+U = Delete current line
Ctrl+K = Delete current line from cursor
Ctrl+W = Delete word before cursor in terminal (Terminal only, also used to close the current document elsewhere)

Arrows up and down = Browse command history
Ctrl+R = History search (Finds the last command matching the letters you type)

Shift+PageUp / PageDown = Scroll terminal output
Ctrl+L = Clears terminal output
Shift+insert = Paste


Create a custom keyboard shortcut
Method1:
shell>sudo  apt-get install xbindkeys
shell>sudo apt-get install xbindkeys-config
shell>xbindkeys
shell>xbindkeys-config

Method2: 
Using metacity (the default GNOME window manager)

1- Open GConf editor (Applications -> System Tools -> Configuration Editor), go to apps -> metacity -> keybinding_commands, and now choose a command, for my example I choose command_1. Edit command_1 writing xkill in order to run xkill (or every command you want to launch like in a terminal).

2- In the same directory go to global_keybindings. Edit command_1 (or the command you choose in part 1) with the wanted shortcut like that : a (to use the windows key just edit the field with Super_L)


ref.:
http://ubuntuforums.org/showthread.php?t=50794
http://ubuntuforums.org/showthread.php?t=79560