Have you ever wondered if anyone is saying anything (good or bad) about your company on the Internet? Or, what are your competitors up to? Google Alerts will send you that information - automagically, and as often as you like.
Yet another free service by Google, their "alerts" are basically memorized searches that will email you the results. Let's say you are insanely interested in Madonna. You can add her name as an alert entry for 'news' and you will get an email (daily, weekly or as it happens) that will contain all news-related items by Madonna. Better yet, the email will be formatted like a search result, so you can easily scan and click only the headlines that interest you.
Since there are potentially unlimited topics to configure as an alert, it's easy to get carried away. But that's ok! Add and remove topics at will. You can also go back and change the frequency of email notifications. Additionally, you can setup the alerts to be sent to a RSS feed reader, like Google Reader.
I have found Google Alerts to be a great tool for filtering the information that I find interesting so I can be more efficient online.