Google comes out with so many cool little programs its hard to keep up. What are the forum members favorite programs off the beaten trail. Google Alerts. It's a great way to find out about new pages indexed, new links, etc.
I still think a lot of people neglect to use Googles Webmaster tools. I think that can be really helpful, especially if you have not fully explored them.
I think google analytics is the most overlooked product of google. Analytics is a must for every webmaster.
I'm an analytics user for sure, and in the webmasters section, i use the info in sitemaps, if there are other tools in that section, i'm oblivious..
You can set an alert for the web on anything, find a unique word or phrase within your pages. allinurl: or site: work well to find new pages, but I recommend only setting it up for a new site, and depending on size, disabling it before you get flooded. link:yourdomain.com works as well, any of the operators that will return results on a web search can be set up as an alert.
I'd have to agree with others above...analytics is very impressive. Conversion tracking, etc. Some very valuable tools that were previously very expensive.
I really appreciate lots of Google stuff (unsurprisingly ), but one thing that I'm surprised not many people seem to know about is Google Search's conversion abilities... e.g.: kilograms in 153 pounds 1200 pesos in usd etc.