Today social media is where most conversations about brands are happening. Knowing who is talking about your competitors is crucial in both seeing how they are doing, and seeing what people think about them, and more importantly finding influencers who care about your industry.
Moz.com has an incredible suite of tools for content marketing, and part of it is social media monitoring which will monitor facebook, twitter, blogs, etc... for links and brand mentions of you and your competitors so you can see who has more share of voice, and who is talking about your competitors. This is a crucial piece to a successful inbound marketing campaign.
Happy Hunting.