Keep up with Google Alerts!
Put in your key word(s) and have Google send you a daily alert whenever those words show up in a news article or blog.
If you are a non-fiction author, make sure to get daily alerts on your book's topic - this will give you an opportunity to follow up with comments or offer yourself as an expert on that subject.
If you are doing marketing research, you will more easily locate blogs & sites that tie in with your subject. You can begin commenting on blogs that focus in your topic's area or are of like minds. You will also discover places that might review your book, do an interview or feature, or allow you to advertise.
So use your Google!