I remember seeing a site that takes (and maintains) snapshots of sites over the years. I've tried googling it, but no luck. Anybody have any idea? Note: This is not software that you install to take snapshots of your site.
Google takes a snapshot of each page examined as it crawls the web and caches these as a back-up in case the original page is unavailable. If you click on the "Cached" link, you will see the web page as it looked when Google indexed it.