Google has a great little tool that (surprisingly) many of the business owners I come in contact with still don't know about.  The tool is Google Webmaster Tools and there are tons of great reasons why you should be using this tool for your website too.  The most obvious is for Google Sitemaps, but let's look at a few additional uses for Webmaster Tools aside from allowing you to add and monitor sitemaps.

1. Keep an eye on your rankings, traffic and which terms are bringing yout he most traffic in a given month (at least from searches on Google)

One of the best reasons to use Google Webmaster Tools is to keep an eye on some of these core website stats.  Webmaster tools gives you insight into your site's rankings for specific keywords, how much traffic you're getting for those keywords (as a percentage, not raw numbers) and many other useful points of data.  And as they say, you can't improve what you don't track.  This is a no-brainer.

2. Determine which keywords to focus on for your SEO and/or PPC marketing campaigns

Since one of the things Webmaster Tools tells you is which keywords you rank for, why not use that info to help guide your SEO and PPC efforts?  For example, if you find that your site is being visited for a particular keyword and your site shows up a few pages deep in the search results, if that keyword is valuable to you, it might be a good idea to focus on optimizing for that keyword to improve your ranking.  After all, if you're on page 3 or 4, you're nearly "in the game".

3. Find out which pages are being linked to from other sites online

Of course, for SEO results, linking is one of the most important factors.  Webmaster tools can show you a "Google's eye view" of which sites are linking to which pages on your site.  And keep in mind that this info is different than what you'll find using the "site:www.websitename.com" search operator.  You'll likely find many more sites linking to pages on your website that show up in Webmaster Tools, even though it's a well-known fact that Google doesn't show all of the backlinks to a site when using the search operator mentioned earlier.  Another part of this tool shows you the anchor test being used to link to your pages too.  Good info to know, especially if you need to reach out to those sites to get your anchor text changed or to provide them with additional content to get even better links to your site.

4. Find out which pages are giving 404 page not found errors

This is also a no-brainer.  Find these 404's, then redirect those links to working pages on your site.  Basic SEO/webmaster stuff, so 'nuff said there.

Now keep in mind that you'll need to verify your site for some of these features to be made available to you (which is a good thing, don't want just anyone to be able to see some of this stuff).  It's pretty simple, just upload a blank HTML file with a filename that the Webmaster Tools interface specifies.  It looks for the file on your website and figures that if you can upload to the site, you probably own it.

Recommendation: Sign up for Google Webmaster Tools, add your site and a Google Sitemap, and check this tool periodically (once a month is probably good enough for most sites).