Google Trends provides some great insight into what people are thinking about, even if they don't always help us to understand what this insight means in terms of the candidates' positioning.
Stories by Thomas Powell and Joe Lima
Blog mentions are, like search terms, something of a special case. They probably show the least conclusive representation of candidate support, because there is no way to assess whether such mentions reflect a preponderance of positive or negative evaluations of the candidates. Anecdotal evidence suggests that negative mentions of candidate A by blogs supporting candidate B, and vice-versa, are very common indeed.