You're British, Canadian, American, Brazilian, French, Spanish, Congolese or anythingish due to gravity and peristalsis. It seems a mite odd to be proud of that*.
Face it, we're generally proud of who we are collectively because we had exactly no choice in the matter, and our patriotism makes up for that absence. In the end, I am proud to be an American and live in America. That agenda's sort of been furthered by getting to visit many different parts of it and seeing many different corners of our great nation. Although I've only traveled abroad once (twice, if you count a one-day stint into British Columbia), and had a great time, by the time the plane landed at home, I was glad to be back.
Lots of terrain, ways and means to visit it, an economy that isn't perfect, but affords the best overall standards of living, is generally just and fair, is imperfect enough to laugh at itself, and allows me the freedom to rip it to shreds one day, but hug and kiss it the next with total forgiveness is a grand place to be. I'm also glad it's not perfect, in a way. You're among the melting pot, the salad bowl, and lots of other food-related praises and insults that intertwine our massive culture. Our nebulous definition of American culture is always changing and undergoing some sort of continuous modification, due to the varying goals and self-made standards in which we fulfill our lives. We also have lots of neuroses that sometimes plague us, a schizophrenia that at once allows us to destroy others, yet be the first to dive in and aid the less fortunate; all the while forgetting that we have dangers and perils at home and forgotten those who've fit out of the scheme of things...culture shocks between the understanding and the completely ignorant; social divisiveness that creates illusory borders and cliques. And yet, we also create more entertainment and more means to express life, art that could fill lifetimes of galleries, sciences that press new frontiers and permit unfettered questions, preserve much of our land for future generations, and technology that seemingly never ends, and a vigilant and unrelenting media that strives to give us whatever we want to know (er, with a side of bias and sponsors/venture capital; hold the laziness, please). Lastly, I don't have to bow to anyone, unless I wish to; I can believe in the awesome power of an imaginary object, bow and kneel to a can of tuna, yet I needn't flinch to any man in greeting, unless I wish to.
All in all, it forces your perspective into a greater scheme of things, that our nation is not the only one, the world is not the only world, and our galaxy is not the only...and so on. I could go on and on, but it's kind of hard to explain, and I don't feel like putting up lots of pictures.