I've been looking for a while for a way to test how different aspects of my websites, e.g. their search ranking, differ from country to country. Normal proxy servers, such as those you can get at xroxy.com, are more often than not slow, unreliable, and worst of all -- tend to get blacklisted by Google and others.
Meet Hide-My-IP: It let's you choose specific countries through which to route your browsing, and does that through private high-performance proxy servers. I'm referring to their paid version ($29) with the "premium subscription" ($7/month) -- the free trial is practically useless.
Give it a try: http://www.hide-my-ip.com/