WebSite-Watcher just released a new version. The program checks an unlimited number of websites for updates and changes within seconds and without much online costs. No site is too big or small for the software. The follow links feature allows you to monitor complete websites, instead of single bookmarks, then automatically insert the linked pages as new bookmarks. When changes are detected WebSite-Watcher saves the last two versions of websites to your harddisk and highlights all text changes. Additional actions when updates are detected, for example to play an alternative sound, send emails or open the changed website with another program.

Im/Export from/to IE/NS/Opera is available also.

Screenshots can be found here.
A 30-Days-Trial can be downloaded here.
You can buy the shareware for 29.95 Euro/Dollars here.