US Classified ads, Forum with US members, Network with US affiliate, Switch IP, Utilize Social Bookmarking Sites.
Visit US based sites and blogs, leave comments to your site on those blogs, and soon the traffic will start rolling in, you can always find out the ip address of the site to find out if it is based in the US or not
Search for the popular keywords based on your site which are used in US and then do work on those keywords. You will get traffic from those keywords soon. All the best!
You can try submitting a Press Release to a site wich is able to distribute your PR to Google News, but you can also try Google Maps to get local US traffic or set up an AdWords campaign if you have some money to spend.
Do article submission only for us sites also classified sites, US local sites, join the us groups in social networking site.
Advertise and write on US-based sites. Such as Squidoo, Hup Pages, Blogger, Facebook, Twitter, etc. Use a webhost that is US-based for your own web sites.
Do local search optimization. That may include getting listed on local directories, using contact us page etc etc.
start posting in us based web directories .. add people on facebook and twitter from united states and when people from usa and also get ranked well in google usa so your traffic can be increased from usa
normally you can't with natural search traffic (your site will be visited by anybody interested in information you provide regardless the country. they may bounce back realizing you (for example ship to US only, or in any other way your site is "US only"). You can only get strict geo targeted traffic when buying it (e.g. from adwords)
Just promote your site in US based links like article,blogs,comment,classified,directory which have .com extension.