Google Sitemap Generator
The importance of getting the sitemap right cannot be underestimated. If you have many pages of content and your sitemap lists every page but one, then you can expect Google to ignore that one page in its listings.
I have found this out on a number of different occasions. Recently I installed a Wordpress plugin which automatically creates a sitemap everytime I write a blog post. Everything seemed fine until I noticed that the blog was dropping in the SERP’s for keywords I knew it had previously ranked well for. I decided to investigate and noticed that my blog had first started to perform badly around the time I loaded the plugin. On checking the auto-generated sitemap created by the plugin I noticed that it had errors (every entry was missing the ‘category’ name in the path) which invalidated every single link to a post on my site’s blog. Google picked up my sitemap and consequently determined that every page that was identified in it did not exist and hence was not indexed. Overnight I lost the ability of my blog content to be indexed.
So, treat your blog with care and make sure that there are no issues with it. If you find there are problems, immediately fix them and resubmit your sitemap to Google Webmaster Tools.