Make the window repaint.

	// Simple script that randomizes the rotation of the Selected GameObjects
	// and lets you see which objects are currently selected
	
	class RandomizeInSelection extends EditorWindow {
	
		var rotationAmount = 0.33;
		var selected = "";    
		function RandomizeSelected() {
			for (var transform in Selection.transforms) {
				var rotation = Random.rotation;
				transform.localRotation = 
					Quaternion.Slerp(transform.localRotation, rotation, rotationAmount);
			}
		}
		
		function OnGUI() {
			for (var t in Selection.transforms)
				selected +=  t.name + " ";
			EditorGUILayout.LabelField("Selected Object:", selected);
			selected = "";
			if(GUILayout.Button("Randomize!"))
				RandomizeSelected();
			if(GUILayout.Button("Close"))
				this.Close();
			Debug.Log(selected);
			
		}
	    function OnInspectorUpdate() {
	    	Repaint();
	    }
	    @MenuItem("Example/Randomize Children In Selection")
	    static function RandomizeWindow() {
			var window : RandomizeInSelection = new RandomizeInSelection();
			window.ShowUtility();
	    }
	}