I am pleased to write my very own but when there is a great PHP script available will be able to just operate on a cron and exclude sites then i'd like to learn about it!

I'd prefer to utilize a scraper/crawler type script than write the XML in the database....

http://code.google.com/p/sitemap-generators/wiki/SitemapGenerators

So far as the database interaction, you are able to adapt among the above.