(a) Classic Tomato (I never vary from that)
Though I'm not convinced about its application in the world of pizza. Mind you, as far as not-so-regular-toppings go, I've also never had the eel topping, nor the crab and peach topping, both of which are rolled out regularly, as specialty pizzas. We also had this really strange one about a year ago, called the 'moving fish' pizza. It was slivers of dried tuna drizzled over the top of the cooked pizza, which actually did sort of float about because they were almost lighter than air!! A true culinary experience a la Hong Kong.