Thanks to Google, we have many free tools available at our disposal. Google Ad Planner is one of them. It helps you identify the top websites that matches exactly the same content and message of your campaign. Furthermore, it tells you if that website is within the Google Content Network which makes your life even easier since you can start a campaign with Google within 15 minutes not just for search but also for Content Network.
Here is a very good reference to more information about Google Ad Planner by fellow Evangelist Avinash!
Once you are in, (all you have to do is to login with your free Google account credentials) You can begin a research to identify the websites. Then you'll need to define the geographic and demographics of your potential customers and the tool filters down the relevant websites. By taking one more step you can even drill down more by adding filters to your target group, such as "find audience" matching a certain website visited or searched a certain keyword.
Let me give you an example; If you want to create a campaign for Peruvians, you can easily identify which websites the Peruvians and/or the people who are calling Peru from US, are visiting in US. This information is very valuable since you have a very targeted audience that you can start your campaign for. The simple way to filter for this group is first to search google for the major news sources in Peru since news sources are the high traffic website for any native countrymen: e.g. "Peru news". Select the top results such as "peruviantimes.com, livinginperu.com/news" and enter them in Google Ad Planner as "sites visited".
Plus also add the relevant keywords such as "call peru", "international calling peru", etc where it says "the keywords searched". There you go; you have a very relevant audience that has the exact geographical and demographic segmentation and has visited the news websites of Peru and/or searched the relevant keywords to make a call to Peru.
Google Ad Planner gives you all the website information along with how significant the audience for each website is and if the website belongs to Google Content Network or not. You can export the list if you want and the best part is that it takes only 5-10 mins to do the initial study. To make your campaign more relevant, you may want to spend more time on the long tail keywords and other relevant websites.