If possible, try to choose something that distinguishes your country from most others, not something that could be said for any countries.
This is next to impossible to do for most modern nations unless they start sticking to the absolutely banal. Like say, wooden shoes for the dutch or beer for the Germans. Those kind of insights are fairly weak I think
Anyway...
First of all since there is alot of America-hate in many international boards I feel that I have to preface my statements by saying that "No, I do not think America has sole claim to anything good or virteous" and "No, I do not always think that America invented everything under the sun". It's sad that I would have to debase myself so much infront of supposably enlightened (atleast compared to us Americans, right?) people - but alas these are the times we live in and loathing of my country has reached a very undeserved high water mark.
The United States. My Personal Top 5 and Bottom 5.
Top 5
1) Habeas Corpus.
2) The Civil Rights Act of 1964 -
http://usinfo.state.gov/usa/infousa/laws/majorlaw/civilr19.htm
3) Social Mobility. This is pretty aptly known through out the world as "The American Dream". Non-Americans scoff at this alot, but it exists. My family and millions of other families are testemant to this. This country has blessed us with almost unimaginable wealth and privelege.
4) Cultural Diversity. There is not a day that goes by that I don't take note of the multitude of people surrounding me of all shapes, sizes colors and creeds. All of us different looking on the outside, but on the inside all striving for the same goal of producing a better life for ourselves and our families. Each man and women entitled to speak their mind, share their views and shape our laws. There is a reason why American citizenship is so prized and its not solely based on money.
5) Beauty. This is personal preference but America is a beautiful and large country. Temperate forests, great plains, coral reefs, blistering deserts, mountains, canyons, artic tundra and rain forests. There is so much to see here that if you love nature you could spend most of your life seeking out new things and never see half of it.
Bottom 5
1) Apathetic voters. People are complacent here because we have it so good. They get soft and seceed too much authority to their representative. To me this is the exact opposite of the principles upon which this country was founded on. A good citizen is a responsible citizen that actively takes part in the democracy.
2) Income disparity. America has a collosal amount of wealthy people, but also has the largest percentage of poor out of any developed nation.
3) Lack of national health care. We have made some inroads on this issue, but its not enough. There is no reason that the wealthiest nation on earth cannot afford to take care of its citizens. Sure, we will take care of you if you are under 18 or over 65, but the years inbetween you are basically out of luck and it stinks.
4) Increasingly stratified education options. One of the best things about this country when it was founded was compulsory public education. Thomas Jefferson said it best when he noted that an educated public made for good voters. Frankly the costs of higher education coupled with the increasing demand of college educated workers is making the situtation untenable. Something needs to be done since we can't keep importing workers from abroad especially when their own countries start to mature and compete economically.
5) Political Partisianship. This is particularly bad in our democracy where we have a defacto two-party rule. Every year the ideology of both parties gets more radicalized leaving a large portion of the public scratching their head and wonder what they should do. It's no wonder that the country is virtually divided against itself when our politicians practice a dogma of actually attempting to divide us!