If your not using webmaster tools, then go and give yourself a talking to. It's free so no excuse.
Google has just added some more functionality. At last you can now get a much more accurate picture of the state of the indexing of your site, which is a lot more reliable than the older way of doing it site:<your domain>
Go into your Webmaster Tools, Health, then you will see a new tab called Index Status
If you select advanced, you can feel for how your indexing is going, how many pages aren't getting selected, potential issues etc.
Have attached a screen shot of our Jobs Vitae website. During early June we realised we had a major problem with our job feed and the way we archived old jobs, so some new coding was done and the issue resolved.
You can see (now in hindsite) the impact of this fix, and how indexing has been resumed as normal.
