This was not obvious to me, although it should have been because the message in the Display preference clearly says it.
Go to Spotlight > “Displays” > Click “Arrangement” tab
Drag the thing horizontal menu bar from one display to the external display and viola the menu bar (and Spaces) appear on the external monitor
omg dude you saved my life. i just bought the 23′ samsung LED 2ms 1080p screen and thought i would have to only use it as a slave :) this made my day!!!
Agreed – this was driving my bats**t crazy. Thank you for this.
Thank you thank you thank you!
You are the guy!
Thank you! Thank you!!!!