there's italian food and then there's pizza.
No one - NO ONE - beats the US in pizza. As someone who has been to Italy many times and tried a ton of different pizza there, nothing comes close to good (ie, not Pizza Hut) American pizza. A local mom and pop or even a high-end regional chain here is going to slap an equivalent Italian pizza place silly.
I've never had lasagna anywhere in the world that can remotely touch what I've had in Italy. Tuscany has an awesome wild boar ragu that is incredible. But the thing you'll notice about authentic Italian sauces is that they use more plain ingredients and they generally aren't as "spiced" (for lack of a better term) as much as sauces we have in the US. I don't think either approach is wrong and both can yield excellent results. I'm not one of those people who go to Olive Garden, hold my nose in the air, and say "Oh, I've been to Italy many times and this isn't authentic!" I appreciate pasta and sauces no matter where I get them and there aren't many truly bad ones.
I saw French cuisine mentioned here - I love it. Duck, foie gras, the various sauces and cheeses - just incredible, even at your average corner establishment. If you get the chance to go to Normandy, try the salt marsh lamb which is raised in the coastal areas (esp. around Mont Saint-Michel).
Regarding American food, I have to agree - we have so much variety and different regional selections that we have to be mentioned too. Our steaks are the best (though South Americans might disagree) and good luck getting a hamburger outside of the US which approaches even a mid-tier chain here.