After Google Trends, another great tool Google offers to online marketing professionals. It's called Google Insights for Search and it allows you to understand search behavior more and more in detail.
Like Google Trends, you can just type in a search term to see search volume patterns over time, as well as the top related and rising searches. You’ll also have the possibility to compare search volume trends across multiple search terms, categories, geographic regions, or specific time ranges.
If you're interested in social media, Royal PIngdom has done a great job using Google Insights to map the most popular social networks and the most ""socially" active countries around the world. For example, it looks like Turkey is the country with the highest interest in Facebook since 2004.
Of course this tool has been conceived to help advertisers who use AdWords, but I personally find it extremely interesting from a sociological point of view as well. For example, see below what Italians have been searching for over the last 30 days.