Error 404. The requested URL was not found on this server.
Have you ever found just the online source you are looking for, copied a link into your files, and tried to come back to it later only to find the page missing? Frustrating! It feels like you have run into a brick wall, but, in fact, there are several ways to find web pages as they used to exist.
Many people know about using the Google cached pages to find a missing page. Other have used the Wayback Machine at the Internet Archive site to find their to a missing source to a source.
Search Engine Showdown provides a very useful list in a post titled Finding Old Web Pages which gives you information on a variety of less well known tools to help you find web pages that have gone missing.
If you have a favorite tool for finding missing pages, please share it below.