Hexagonal Grid allows you to create a hexagonal grid.
Editor: Unzip the file and place the DLL file in your C:/Program Files/Paint.net/Effects directory.
(Re)start Paint.net !

This is a new plugin that will be under the menu Effect/Render.
It allows you to Create a hexagonal Grid.
The grid is centered on the Middle of the picture (or selection).
You choose the grid size (1 to 1000, Default:100).
You could choose Between six drawing mode (see the UI).
You choose the brush size (between 1 and 100) with/without anti-aliasing.
Not so much to say about it...
Oh, BTW, thanks to Boltbait for anti-aliasing code... you can free download Hexagonal Grid 2.0 now.