Google Webmaster Tools introduced a new feature around few weeks ago. It’s called Index Status. I was taking a look at it today and it can really help you to identify any search indexing related issue for your website. Index Status is under Health menu. When you click on it you should see a graph like below that will give you the total number of webpages indexed in Google search of your site for every week over a period of time. So if you see that your graph is rising steadily then you can rest assured that all is well and your new pages are getting indexed by Googlebot regularly.
But this data might not be enough for you if you try to find out more sensitive problem in your website. For this purpose, you can use the Advanced tab at the top. When you click on it, you should get something like this:
And it will give you all the details like number of pages not crawled because they are blocked by robots.txt or the number of pages not selected for inclusion in Google results as you haven’t followed standard procedures while restructuring your permalinks.
So just check this feature and monitor it regularly. It can be a real help to debug site related issues.