Check Multi Sites
This tool will take a list of URLs (from the same or different sites) and fetch the HTML for it. This will store the report so you can do things with it.
After you make the first request, you will get a report ID and a URL to revisit the report. Once you revisit the report you can run a compare between the versions of the sites you listed.
You will at the time get an option to "Save Compare", once you have done save compare you can actually view the thumb nails of the sites
Location:
http://sitepreview.ourace.com/validsites.php
Screenshots
Initial Scan:
Initial scan using URL with Report ID
Compare of both using save Compare option
Looking at saved report via report URL. Clicking on 1 to see the diff
