Google Now Shows Your Indexed Pages
Using Google Webmaster Tools, you can now see how many pages of your site are actually indexed by Google search engines. This is helpful in determining the payout of SEO efforts and other reasons.
You can find it here:
And here is an example of a domain’s index status. As you can see, some major changes done to the SEO of the site affected the number of pages that were indexed in May of 2012 dramatically.