This is something I wanted to create for several months, and I recently finished it.
It introduces beginning programmers to C# by showing them how to build a very simple RPG (no graphics, very few features, etc.)
I know it won't appeal to 99.999% of HN readers, but it's something I'm proud of, and wanted to show off.
http://scottlilly.com/learn-c-by-building-a-simple-rpg-index