Paint.NET is raster graphics software that can be used to design and manipulate raster images. It is basically either a souped-up version of MSPaint or a simplified version of Photoshop/GIMP depending on your perspective. It is very useful for simple edits to photographs and other raster images.
Paint.Net is free software, anyone can download and install it for free on their personal computer.
Install Link: http://www.getpaint.net/download.html
Tutorials and information can be found at http://forums.getpaint.net/index.php?/forum/18-tutorials-publishing-only/.