Google Webmaster Tools is a very helpful way to monitor how Google is reading your website. After you have verified owner ship of your site by uploading a file or meta tag, you can provide the address to your xml sitemap and then monitor a number of things, including: top search queries, links to your site (often an incomplete list), crawl errors, keywords, and the status of your sitemap.

Google Webmaster Tools can help you tweak your robots.txt file so you can better control which files at your site should NOT be followed and indexed.

There is also a malware detector, crawl stats, HTML suggestions, and a site performance monitor that tells you how fast your site downloads in comparison to the rest of the world wide web.