Online trackers for web page changes 
Web sites that will monitor a list of web pages and notify the user when changes occur. Possible evaluation criteria: ease of use, customizability of results (searching only for specific changes), form of notification (e-mail, RSS), and cost.
Resources
Track any website, whether or not they support RSS. An e-mail is sent with customized frequency.
Allows scheduling checks at specific times or days of the week. Features keyword matching to decide whether a given change merits notificaiton. Free.
ChangeDetect is a free service that saves your favorite web pages, monitors content for changes and sends an automatic email notification to you whenever your web pages are updated. Receive web page change notifications on your email, pager, ICQ or text messaging device. ChangeDetect marks web page text for you with color-coded highlights of what has actually changed.
Drag-and-drop button on your browser toolbar. Complicated registration but manages bookmarks like spurl.net
Feedwhip is great - good customizability and interface, and it now has RSS feeds. Premium accounts are free for a limited time.