The students in my digital journalism class created screencasts for a number of different Web 2.0 tools.
Here are two of my favorites:
1. Shelfari - A social network for people who love books
You can use Shelfari to find good books to read, review the books you have read, discuss your books with others and more. Check out this screencast by Agazi Desta to learn how to get started.
2. Webs - Create your own Website for free
This is a great tool for not only creating Websites but also creating communities. This would be a great alternative to Ning as it includes the option to create a discussion forum on your site. Arien Woodrow made a screencast that shows you how to get started using Webs.