Google Webmaster Tools (formerly Google Sitemaps) is a development by Google allowing webmasters to easily provide Google with more information on what pages to index, when they have been updated and generally making a site more Google-friendly for indexing and listing within Google search results.
A ‘Google sitemap’ is an XML based file which Google crawlers access on a frequent basis to check for new pages and updates to pages. Ideally you want to have sitemaps created on the fly or by overnightly tasks – this ensures Google is kept up to date on a daily basis. All published pages are listed within the sitemap file with the last modified time.
The SEOSolutions sitemap can be viewed here: http://www.seosolutions.co.uk/sitemap.xml
In addition to sitemaps within the Google Webmaster Tools there is other interesting data available:
1. Data relating to top search queries for your site
2. Information on last website crawl by Google
3. Website errors experienced by Google when traversing your site
4. Web page analysis
5. Index stats
More information on Sitemaps and Google webmaster tools can be found here: http://www.google.com/webmasters/sitemaps/