A worker carries a pizza for delivery as he exits a Domino's pizza store in Sydney, Australia, Aug. 12, 2015. Reuters

You love pizza, but if you eat pies with only cheese and pepperoni, you might be limiting yourself. Sunday is National Pizza with Everything (Except Anchovies) Day. Sure, it's not exactly up there in the holiday upper echelons alongside Thanksgiving or Christmas, but do you really need an excuse to try new pizza toppings?

Americans eat about 2 billion pounds of pizza cheese each year. If you're looking to expand your culinary horizons, we like olives, sausage, barbeque chicken, arugula, peppers, onions, mushrooms, bacon and pineapple on our pizzas, just maybe not all at the same time.

In Brazil, pizzas with green peas are popular, while the French eat fried eggs on their slices. In China, a crust made of mini-hot dogs is a favorite. Hawaiian pizza was invented by Sam Panopoulos, a native of Greece, in 1962 in Canada.

To celebrate with pizza from the nation's top three pizza delivery companies, search for online promo codes for Papa John's, Pizza Hut and Domino's. Here are some coupons we found online. If one doesn't work, you can keep trying other retail codes until you get lucky.

Domino's: You can get two medium 2-topping pizzas for $5.99 each with the promo code 9193, according to Deal Catcher. You can get a large 3-topping pizza for just $7.99 when you apply the promo code 9174 at checkout.

Pizza Hut: You can get a medium 3-topping pizza for $6 with promo code TEOMED3T6, according to Deal Catcher. Pay $10 for any large carryout pizza, according to Pizza Hut's website. Pay two for $5.99 on select items with code 9193, according to Retail Me Not.

Papa John's: Save 25 percent off regular menu price items with promo code 25visa, according to Deal Catcher. You can get 50 percent off your online order using code kcchiefs, according to Coupon Follow.