Software to monitor indexed pages

[JorisHas]

Dear SEO moz,

As a SEO marketer on a pretty big website I noticed a HUGE amount of dropping pages indexed by google.

We did not do anything to block googleblot in the past 6 months, but since November the number of indexed pages decreased from 3.4 milion (3,400.000) to 7 hundred thousand (700,000).

Obviously I want to know which pages are de-indexed.

Does anyone you know a tool which can do this?

[irvingw]

We have a large site too and we have different sitemap.xml files for different sections of the site and submitted in WMT where we can see which sections are having indexing issues under WMT > optimization > sitemaps

Maybe that is a good thing though, do you have 3.4 million legit pages or are dupes getting filtered out? Has anyone changed your parameter handling or coding on the site URLs, or robots.txt file or noindex meta tags?