To check us ranking go in toolbar click on the arrow next to the google search button, it will give a drop down to choose google images, patents, finace, more. In more there will be globe icon with USA button withit. I use to use proxy for checking rankings and its the same majority of the time to the results i got from the option I mentioned. Also you can use AOL as its show US results also. Just my 2cents, wont say that this the definate way or anything, but works for me a'ok.
If you are out of US country then go to google.com and search your keyword then add "&gl=us" in the url at the end and again search. Second method, go to google.com then go to advance search option, then click on "Date, usage rights, numeric range, and more" and select US country from region. Now search your keyword ranking.
quickly check your site's Google Page Rank, Alexa Rank and may more here - http://popuri.us/ May be helpful to you.
My website (http://www.go2store.com) gonna be launched in next month. Could you please tell me more for details. Thank you,
u can go alexa.com and install alexa toolbar and you chek your website trariff rank in usa. and you also use google pagerank checker to check your page rankig in usa.