Webmon is a free windows based software which allows you to check unlimited number of sites with an interval of a day or may be every few minutes. This makes sure you get the update as fast as possible instead of waiting for the newsletters.
What I even more interesting was that it even lets you watch if any particular text changes on the page. It downloads the HTML of the page and then you can set which change you need to track. This makes it extremely powerful checker. Also you can specify to check between words or paragraphs.
You can use it to check if certain words appeared on a webpage or use it HTML downloader or simply just check if the website changed its content. Find out more on WebMon