How to move windows around and between monitors, using keyboard short cuts?
The Put Windows extension implements this feature. After installing it, Super+Shift+Left and Super+Shift+Right move the active window to the previous/next screen, respectively -- just as in Windows. This works even in a three-monitor setup, and also moving maximized windows now works reliably.
Frychiko's solution works great in a two-monitor setting but suffers issues when moving maximized windows.
Tested with Ubuntu 13.04.
In Ubuntu 17.10, the Shift+Super+Arrows keyboard shortcuts move the window between the different monitors.
Can be modified under Settings > Devices > Keyboard > Navigation > Move window one monitor up/down/to the left/to the right.
Ctrl + Alt + NUMPAD 4 (left edge) Ctrl + Alt + NUMPAD 6 (right edge)
Make sure you are using the NUMPAD cursor keys, not the dedicated ones, if you have those. Otherwise, it'll switch workspaces.
Note that these shortcuts only work on non-maximized windows. Un-maximizing any selected window can be done using
Ctrl + Alt + NUMPAD 5 (center)
List of Unity keyboard shortcuts here in case you haven't seen them.
What are Unity's keyboard and mouse shortcuts?