For Google: Google Alerts (email or RSS updates of the latest Google search results)
For Blog
posts: Technorati (the largest blog search engine)
For Blog comments: Backtype (what people say about you in response to blog posts)
For other social media: FriendFeed search, a social aggregator that combines YouTube, Delicious, Flickr
and more.
Click here for 8 easy ways to track your property's online reputation.