Radian 6
With the Radian6 listening platform, you can monitor the social web. Find your brand on millions of blog posts, viral videos, reviews in forums, sharing of photos, twitter updates.

Features:
Scan millions of sites including blogs and comments, photos, videos, mainstream news, forums, and micromedia like Twitter and Friendfeed

Pros:
Nice-looking customizable interface with reporting from entire social-sphere, that also includes web analytics. Partnered with Salesforce and build a strong CRM that is easily accessible to both agency and client.

Cons:
Results are based off key words, does not offer much insight into text analysis or human language processing (sentiment).

Pricing:
$600 – $$$$/month depending on need