Connecting MacBook Pro to multiple monitors, one in portrait (vertical) mode
Yes, simply go into System Preferences->Display.  A new window will pop up on your primary monitors, as well as your external monitors.  The external monitors should have a "Rotation" drop down menu, in which you can select "Standard", "90º", "180º", and "720º".  If you select "90º" and hit "Scaled" under the resolution option, you'll see that the standard width and height are all swapped, and that 1080x1920 will be the default option (but you shouldn't have to set it to scaled. Default for Display is probably the best option).