I'm running a windows 7 laptop ... so I tried it .... pressing ctrl+alt+ the left arrow flips the screen image 90 degrees counterclockwise. Pressing the right arrow will flip it the other direction. Pressing up arrow brought it back to normal.
(Not sure what happens when I reboot.)
I just showed my tween this cool new trick, without showing the key sequence, and he says, "ctrl+alt+arrow key ... I've known that about 2 years, dad