Web Secretary is a web page change monitoring software. It will Detect changes based on content analysis, making sure that it's not just HTML that changed, but actual content. You can tell it what to ignore in the page (hit counters and such), and it can mail you the document with the changes highlighted or load the highlighted page in a browser.
Web Secretary is actually a suite of two Perl scripts called websec and webdiff. websec retrieves web pages and email them to you based on a URL list that you provide. webdiff compares two web pages (current and archive) and creates a new page based on the current page but with all the differences highlighted using a predefined color.