WayBack Machine is a free Chrome extension which detects HTTP 404 and other "missing page" codes, checks to see if an archived copy is available at the WayBack machine and offers you a "click here to see the archived version" link.

This system won't always work. If the site detects and handles the error code itself, maybe to give you a custom 404 page, WayBack Machine's extension won't see any problem or offer an alternative.

When you do get a message, it doesn't give you a choice of previous versions. We think you'll just get the most recent available version of that page. However, you can move to another WayBack Machine snapshot by using the regular selector at the top of the screen.

On the plus side, the extension doesn't get in your way, won't take any action unless it detects an error code, and in our tests it's very speedy. We were usually alerted to available copies of a missing page within a couple of a seconds.

A sizeable group of people have reported that the extension doesn't work at all for them, so there may be a conflict with something else. Check it out with the official test page. If it works there, it should work anywhere; if it doesn't, it probably won't work at all.