Another option might be to drag your Model into your ArcMap session, which creates a Tool Layer in your TOC, a special kind of Group Layer that you can use to run your Model and automatically add the results to the map display. This option does come with its own set of complications, however, so you should read the Help doc about it before deciding whether or not to go this route. For one thing, the Model is not actually resident inside the Map document, so if you want to share it with anyone else, you still have to provide both the Map and the Toolbox that contains the Model, and whether or not you choose relative or absolute paths can become a critical issue. Also, subsequent edits you make to the Model may not have any effect until you remove and re-add the Tool Layer in the Map. And I think you still have to declare those model outputs as model parameters before the Add to Display setting will have the desired effect. Finally, even if you are giving those outputs unique names every time you run the model, in your TOC they will always pick up the label of the Model object (variable) that represents them, so only the most recent results are automatically displayed, and will replace previous results unless you have changed the layer name in the map TOC.
A related question: I have tried all permutations to get an output Table to automatically Add to Display and nothing works, even though the Add to Display option appears to be available on output tables in Model Builder. Perhaps ESRI simply forgot to "gray out" that option for table objects in the Model. Does anyone know?