Paint.Net is an excellent free image editing program for Windows. Released in 2004 as a school project the program has grown steadily over the years into an excellent mid-range image editing program supporting layers, effects, transparency and more. It’s what I use for creating documentation, basic web graphics and quick basic image editing. Perfect when Microsoft Paint isn’t enough and Photoshop is too much. Did we mention it’s free software?
Forums for support and questions: http://forums.getpaint.net/