Google Webmaster Tools
From Lunarpages Web Hosting Wiki
Google's Webmaster Tools is something that every webmaster should look to joining up to, especially if you are concerned about how your web site is doing in Google.
By using this series and set of tools you can see all kinds of information about what keywords are bringing people in from Google, the Google crawl rate, the last time your page was indexed plus around two dozen more cool tools and interesting resources. If your a webmaster who hasn’t done this your missing out on a free set of very helpful tools right from the Google team.
One problem you might run into after getting signed up and logged in for the Google Webmaster Tools is how do you get a “Google-friendly” sitemap setup? Here are a few suggestions to get you started in that department:
After you get your domain and your sitemap in the system then you must verify that you are the owner of the web site. You can do this either by adding some code to your index's header information or by uploading a file with a funny name. I would say go with the second one as it is the easiest one to do. Create your file with the funny name on your desktop, upload it to your “public_html” folder and then check to make sure it is there. Then you can go back to the Google Webmaster Tools web site and tell Google to check for verification.
Some of my favorite webmaster tools (once you get things up and running) would be:
404 Finder - They will give you all of the 404’s that Google found while trying to crawl around your web site.
Crawl stats - These statistics provide distribution information for pages they have crawled for the index.
Analyze robots.txt - Makes sure that Google can read and understand what is inside of your robots.txt file.
URLs Submitted - Once your sitemap is crawled, Google will let you know how many URLs exactly they know about.
There is no doubt that this is something everybody out there with a web site should be doing. Even if you don't track the data every single day - it is nice to have when you need it.