Visualping - Visualping is the easiest to use website checker, webpage change monitoring, website change detector and website change alert software of the web. Read more about Visualping.
Archive.md - archive.is allows you to create a copy of a webpage that will always be up even if the original link is down
Distill Web Monitor - Distill is a web monitoring tool. It can monitor RSS feeds, a webpage or a part of webpage. Alerts in the form of pop-up, audio or emails can be received.
Wayback Machine - Browse through over 150 billion web pages archived from 1996 to a few months ago.
Wachete - Track web page changes and get notified. Free Sign-up. Have all data in one place
Perma.cc - Perma.