Well, you could always pick one or two big attractions like Vizcaya, Coconut Grove, Coral Gables and the Biltmore, etc., but it will be hard without a car. If you want a very quick overview, you might want to try a DuckTour: http://ticketing.ducktoursmiami.com/...tegory.asp?c=2. I've never done the one in Miami, but I've heard it's popular, and I went on one in SIN once and enjoyed it.