In addition to the official Microsoft sites for the product, there are also sites created by independent professionals and Microsoft development staff.
Before Microsoft came out with the official community site, there were already dedicated fans of NAV that created their own forum. At the time of writing, the most popular non-official Dynamics NAV forums are:
www.mibuso.com: This is one of my favorite Dynamics NAV forums. The primary reason I like this forum is because I like phpBB style forums.
dynamicsuser.net: This is another forum that services the Dynamics NAV community. This forum has also expanded to service other Dynamics NAV products.
Both of these forums have dedicated experts to help out with user questions. A lot of the users frequent both sites, so you can get your questions answered on both sites.
There are a lot of blogs out there, but most are not that useful to further our education in Dynamics NAV. Some blogs that are the my personal favorites are:
blogs.msdn.com/b/nav: This blog is maintained by the Microsoft development team for Dynamics NAV. You will be able to find detailed information for every undocumented feature in the core product (real features, not bugs) here. If you're serious about Dynamics NAV, this site should be bookmarked or subscribed to your favorite RSS reader. The information posted here, even though it's from Microsoft employees, is not officially supported by Microsoft, the company.
www.waldo.be: This blog is written by Eric Wauters, a Dynamics NAV MVP. His blog has been one of the community favorites for his updates on the latest and greatest from Dynamics NAV.
navigateintosuccess.com: This blog is maintained and written by a former Microsoft employee, Vjekoslav Babić. He has been a valuable contributor writing about new technologies that deal with NAV.
www.dynamicsnavconsultant.com: And last but not least, this blog is written and maintained by Alex Chow, the author of this book. This blog documents Alex's journey in Dynamics NAV, talking about more functional and business-related topics pertaining to Dynamics NAV instead of technical topics.