To shop from the United States, I've been using a free package forwarding service from Viaddress.com for a few months now, and I'm quite satisfied with them... I used them to shop on Amazon.com and Ebay.com and it works great!
The registration is free and they provide you with a personal US address that you can use to shop from any US merchant and have Viaddress forward your packages to your country.
If the US merchant does not accept international credit cards, Viaddress can buy the products for you, with no commission fees, and then forward the packages to you. Their prices are very competitive; u can log unto their website to see their price comparison chart.