Of course, this is such a classic dish.  Admittedly it is super easy.  However I add it here because I feel that to get the ultimate result for this you need absolutely the freshest of ingredients.  I use basil straight from the garden and cut it on top shortly before I serve to preserve the flavor and to keep it from discoloring.  Use home-grown, or the best beefsteak tomatoes you can find and naturally, fresh mozzarella.  Extra virgin olive oil is a must.  I have also drizzled a small abount of reduced balsamic over the salad in the past for another twist.