how to rotate the orientation of my monitor in OSX 10.8?
After some research i found this blog, which perfectly detailed explains how to get this hidden setting:


Open the system preferences
Hold down the command and option keys while clicking the display
icon
Next locate the screen adjustments on the external monitor and you
will notice now there is an option called "Rotation".
Choose 90 Degrees and now your monitor is in portrait mode.


Thanks roadzy and OSXdaily!