Nice working list of ingredients you guys! I use and/or have tasted pizza with the following and enjoyed them:
There's parmesan and then there's
Parmigiano-Reggiano. Accept no substitutes!

Pecorino Romano
Montegrappa (not as salty as Pecorino, less nutty than Parm-Reggiano, earthier than both. A nice cheese)
Piave
Mascarpone
Smoked Mozzarella (
http://www.mountainmozzarella.com/products-smoked-mozzarella.htm) pairs with red onion very nicely
Porcini Mushrooms (particularly good with Thyme. The water from steeping the shrooms can be interesting when added to the dough itself when kneading)
Hen of the Woods Mushrooms
Grilled/Marinated Portabellas
Roasted Corn (good with goat cheese and another, saltier cheese)
Squash Blossoms
Sauteed Eggplant
Leeks
Eggs (sunny side up)
Quail Egg
Figs! (Paulie Gee's marscapone and sliced fig pizza was one of the biggest pizza eye openers of my life)
Orange Blossom Honey (again good paired up with marscapone and/or goat cheese)
Nutella (I had this with fresh pears on a pizza while in Italy....very good)
Speaking of seasonal, the Dolce e Salato (pumpkin, ricotta, sage, amaretto, sausage and parmesan) at Iggies is not too shabby
http://www.iggiespizza.com/ Speck (smoked bacon)
Guanciale (pork cheek. quite tasty)
Culatello
Mortadella (needs to be shaved
thin on pizza)
Soppressata
Bresaola (beef salumi product aged with cloves and laurel. had it on a pizza with shaved Pecorino and a drizzle of aceto balsamico tradizionale added post bake back when I ate meat. Very good and the dough was nice on this pie)