I just love pizza, man, but you can't go wrong with black olives. They're my absolute favorite. Other hits include mushrooms, red onions, chicken, and cheese. Lots and lots of cheese.
Pepperoni and Ground beef. My boyfriend won't even try new pizzas anymore because he says its disappointing compared to this. Normally he wants to try everything new!
Say what you will but I think I do prefer simply pepperoni. I've never liked pizza that was loaded down with a bunch of stuff, and I never liked the flavor of a ton of toppings or the unpleasant heaviness of pizza with like, 5 meats on it.
I do like pepperoni and jalapeno, but I get hit pretty hard with hearburn in that case to where I may not do that anymore...sometimes meatballs are really good too if you want a little extra meat but aren't into the sausage. Sometimes grilled chicken is good, too. Don't usually mind red peppers but I probably wouldn't ask for them.
There used to be a small pizza place where I lived that put small fried potatoes (basically tater tots) on the pizza...that was also pretty good.