I wouldn't say sweetcorn is a common toppings in Europe. I guess the biggest difference is the type of cheeses they use. Some people like truffles, but i wouldn't say it's common.
Oregano is quite common with pizzas that include sliced tomatoes. So is garlic, tons of it. Prosciutto is great when combined with the right chese. It can make or break a pizza. Basil is pretty common, too.
I saw a few pizzas with eggplants on them. Still recovering from that. Same with eggs (think carbonara).
I have mixed feelings about artichokes.
I've seen tuna a few times, but i wouldn't say it's common.
Another thing that divides the pizza world in my experience is the inclusion of olives.
Three questions come to mind (my pov in brackets):
Yes or no? (depends on the type of pizza but yes)
Black or green (depends on the cheese and toppings used)
With or without nut? (if you pick the latter please kill yourself)
Don't even suggest sliced olives. Just don't.