A number of tools can help you find and manage mentions of your company online:

backtype.com
WHAT IT DOES: Sends you alerts when a comment is made that includes your company name or brand

blogpulse.com
WHAT IT DOES: Searches blogs for mentions of your company

boardreader.com
WHAT IT DOES: Searches message boards, forums, videos, and Twitter...

List continues here: Online Spying. The Good Kind - BusinessWeek