In order for you to download various apps from US iTunes Store, all you have to do is to create an iTunes App Store account for US Store. (I'm going to explain about creating an account in US Store, because most of the apps are available in US. But you are free to try UK or other countries as well). As you may know, to create an account, iTunes Store requires you to provide a valid billing address and a credit card information in the country you choose. I'm going to explain you a workaround. There are two ways to do this, one is to do it from your iPhone/ iPad or other iDevices or do it from your Computer. Both ways are similar, so I'm going to explain only on creating an account from your iPhone.
Creating an App Store account with no Payment option from your iPhone
Sign out from your existing account by going to Settings >> Store >> Click on the Apple ID. Once signed out, go to App Store on your iPhone and search for Google+ or any other free iPhone apps and click install. You'll be asked to enter your App Store ID or create a new one. Click on Create new and select United States as the country. Once you agree the terms and conditions and your account details, you will be asked to enter Payment information. By default Visa is selected. Click on this and select "None" from the dropped down menu. Please note that you will see "None" option ONLY if you select a free iPhone app and try to install it. If you choose a paid iPhone app and create a new account, you will not see the "None" option, but to enter valid credit card options or PayPal account information.
After you select "None" and provide a valid address in US . Once that is done, Apple will send you an email to verify the email address you provided. Go to your email account and click on "Verify Now". You are done. You have just created an App Store account in US iTunes Store!
Go to App Store on your iPhone and download Google+ or any other iPhone apps that are not available in your country. There are 100s of cool iPhone apps that are not available outside US store, like OneNote from Microsoft. I love OneNote on my computer, but the iPhone app is available only for US customers. By creating an account as I explained here, you can download OneNote app as well.
Creating an account from your computer is also similar to what I've explained above. All you've to note is that you must try to install a free iPhone app and not any paid app, only then you will get the "None" option in Payment options.
Do you have any other ideas to download apps from other country's iTunes Store? Or have you already been using this method and facing any difficulties? Please share it with us in the comments area...