1) Resilience. It's written into our Constitution - the Founding Fathers didn't believe in free lunches and as long as we keep that basic point in mind I think we'll do okay.
2) Openness. Bloated bile-spewing gasbags like Michael Moore can weave together anti-American screeds one after another, each more vile and delusive than the last, make a big buck off of paying customers, and never ever ever have to worry about black sedans pulling up to his house at 3am to whisk him off to some dank basement for the rest of his short life.
3) Identity. America stands for something: liberty. It doesn't always live up to the strictest standards of that vision, but we try - we always try. I've learned that relatively few citizens from other countries believe their countries stand for anything or indeed should stand for anything. I think this works against them.
4) Power. This nation can be picked at by cave-dwelling barbarians for a while or outright annihilated by a nuclear power like Russia, but it can never be overpowered.
5) Variety. Geographically, culturally, and socially, we've got a little bit of everything.