I distribute a free DotNetNuke Google SItemap generator on my site. It is an extensible model to handle modules where you can generate all the various 'child' links for a particular page. Most commonly, this is for pages where you have a module installed, like the Blog Module, News Articles module, or the Property Agent module. These types of modules use query strings in the Url's to show the correct pages, and the 'standard' sitemap generators available either don't generate all the links, or only do them for a particular module.
The solution I distribute can be endlessly customised for *any* third party module in DotNetNuke, just by creating a new Sitemap Provider for the required module. So far I have providers for the Blog Module, Ventrian News Articles module and the Ventrian Property Agent module, plus providers for my own Tagger module. The source code and instructions are provided to build your own providers for third party modules, or, if you don't have the skills or the time, you can get me to build one for you.
The Sitemap and information is available on this page :iFinity DotNetNuke Google Sitemap Provider
To answer another previous question, the limit for a sitemap is 10,000 urls, but you can have multiple sitemaps and a sitemap index file, theoretically giving you unlimited sitemap entries.