It was quite close. This works:
import PythonQt
selectionSuccess = PythonQt.BoolResult()
selectedItem = PythonQt.QtGui.QInputDialog().getItem(None, "MyTitle", "Label", ['Choice1', 'Choice2'], 1, True, selectionSuccess)
Note that popup windows are generally very annoying for users and should only be used in exceptional cases. I would recommend to add these widgets to your module’s GUI panel instead (by using Qt Designer).