The most obvious way to get a sense of the scope of your topic, and some ideas for what to focus on, is to look at the German version of Wikipedia (if you haven't used it before, it's at wikipedia.de.) Like the American version, you can search it by keyword and find articles on most common subjects. You'll also usually find some links to related sources where you can find still more information.
The next most obvious is to search the German Google (Google.de). You'll get everything from news pages to blogs to youtube videos to jokes. Much of it will be of dubious reliability, but for some topics the sense of what people are thinking and saying is very important; even if they don't have their facts straight. But you'll also come across some excellent sites, like the Goethe Institut site on German reunification.
For more substantive sources, click on the next tab.