How can I choose an iOS simulator as the destination in Xcode?

For me the problem was that the selection in the toolbar only shows up for a certain width of the XCode window

There should be a menu in the top left region of the toolbar section of the IDE. It should have a run button, a stop button, and then the name of your app and a label saying IOS Device. Click view-->show toolbar if you don't see it. Click on IOS Device and you should get a drop down menu of devices. The simulator should be in that list.

This should do it, its very simple actually

Just in case anyone finds this helpful --

Sometimes your version of xCode doesn't support the deployment targets.

My iOS simulator did not show up as a destination until I set the deployment target down to 7.0 (it seems like 7.1 may not be supported by xCode 5.0, but only 5.1 [not confirmed]).

Hope that helps if anyone stumbles across it.