although not a Joomla component - this is by far THE best xml sitemap generator I have ever tested.
http://www.xml-sitemaps.com/standalone-google-sitemap-generator.htmlBest of all, updates are free and you can use it on any and all of your own domains and it is cheap $20. They have an affiliate program but to show my unbiased oppinion the above link is a straight link to purchase it.
sample of xml sitemap from JoomlaViews.com:
www.joomlaviews.com/sitemap.xmlAs you can see, all links are sef advanced, as it actually crawls and it pings Google, LIVE and Yahoo when done and it can run in the background and I am 99% certain you can even cron it, don't see any reason why not and it is not a resource hog either, and should it drain your server, you can set it to wait every x seconds/minutes/pages.
--Tone
Yes, I'm using it in all my websites with Sef advance (some of them are large with more than 15,000 pages). I'm using cron to generate automatically a new sitemap.xml everyday. This script ping automatically the more important Search Engines. You can install in less than 5 minutes.
One of the best investment I did. Works very well. In one word "Amazing"!