A good article on using Google Sitemaps - http://www.sitepronews.com/archives/2006/july/3.html http://www.smart-it-consulting.com/article.htm?node=163&page=113 http://www.automapit.com/signup.html http://code.google.com/sm_thirdparty.html http://www.xml-sitemaps.com/
They sell a cheap one on ebay, from jeremy burns, (I think) and it works well for smaller sites. Perhaps not best, but for the money for something hard and fast......
I vote for self (obviously) However, that said, you should probably consider trying multiple tools to compare xml sitemap features etc.