Okay, I'll concede The Internet for the technical reasons you mentioned. And poo poo Facebook/Twitter all you want, but they've created substantive international social and cultural changes. Shallow though they were, political ones too (Arab Spring). And while CERN gave us The Internet, America gave the world Amazon, EBay, Wikipedia, Google, YouTube and Napster (I mention Napster because it single-handedly turned the music economy on its ear).
Not to mention, there's a reason why Apple (world's most powerful/valuable brand) has products on display in museums.
And sure, for the most part we eat like idiots. But we're also producing celebrity chefs and food concepts at an outrageous clip right now. We've also been home to the "Best restaurant in the world" (Alinea, Chicago). As a Chicagoan, I must interject the importance of food in our culture. As this is a Buffalo-centric message board, it's something most here could/should understand. It aint all Ho-Ho's and Lucky Charms, but I get your point.
You mention baseball, but gloss over other uniquely American sporting cultures like football, anything pertaining to college sports (not least of which: March Madness), and the fact that we continue to kick the world's ass in the Summer Olympics.
Just because you might not "get" other things like video games, doesn't mean they aren't culturally significant, too. Newer games like BioShock Infinite are pushing the boundaries for what an entire medium can do.
We also have guys like Tracy Letts writing some DAMN good plays right now.
I mentioned it briefly, but shows like The Wire, Arrested Development, Breaking Bad, Mad Men, we're in a television renaissance right now.
Music: yeah, I dug a little deep, but you completely ignored hip-hop. Again, an entire GENRE born and perfected here in the United States. We also have contemporary bands doing great things with styles of yore--guys like Robert Randolph and Derek Trucks (though he benefits from some pretty sweet lineage).
How about experiential culture like amusement parks and festivals? Our country is lousy with those!
I understand we had some pretty big cultural breakthroughs in the first half of the 20th Century. But we live in such a fragmented age right now that it's bogus to say "nothing" has happened since The Beatles appeared on Ed Sullivan. If Ed was up against 1,000 other channels, YouTube, video games, and the entire Internet at large, I think we'd be a bit less romantic for how we perceive the cultural "significance" of events that happened during a time when not a lot of options existed.