How to move windows that open up offscreen?

For Windows 7 and later users: +Shift+← or → will move the selected window to the monitor in that direction.

I use this approach:

• Use Alt+Tab to switch to the off-screen application.
• Press Alt+SPACE to bring up the system menu (you won't see it because it is off screen)
• Press R to select the "Restore" menu choice to ensure the windows isn't maximized (you cannot move it if it is maximized)
• Press Alt+SPACE again, then M to select the "Move" menu choice.
• Press one of the arrow keys to initiate the movement.
• Now just use the mouse to place the window where you want.

If you are using a non-English version of Windows, the "R" and "M" menu choices will probably be different.