1. All the Americans I've ever met personally in America, with one uniquely horrible exception I won't discuss here because this is a "favourite things" thread. Besides, his compatriots obviously didn't like him either. Americans at home, in my experience, are the friendliest, most helpful, kindest, most accommodating people on the planet. It's a great place to visit, and I'm pretty sure what I'm seeing there is the self assurance and confidence that comes from being the wealthiest, most powerful nation in the history of civilization.
2. They way they've preserved and publicized their history and heritage. You can't go anywhere in the states immediately south of where I live, for instance, without finding plaques and historical markers and preserved sites about the Lewis and Clark expedition, and the level of detail is amazing. There's probably a record somewhere of everywhere Meriwether Lewis stopped to take a leak. You will look in vain on the Canadian prairies for any significant mention of people like Henry Kelsey and Alexander Mackenzie and John Palliser. We in Canada have done a terrible job of promoting such things, which probably has something to do with our national identity crisis and our continuing need, in some circles at least, to bash the U.S. We don't know who we are, we just try too hard not to be somebody else.
3. The U.S. Declaration of Independence and, more broadly, the Constitution it's a key part of. Those are extraordinary political documents, unique in the world as far as I know, as a working embodiment of the best, most enlightened values of the Age of Reason.