Originally intended as a free replacement for the Microsoft Paint software that comes with Windows, Paint.NET has grown into a powerful yet simple image and photo editor tool. It handles most of the basics you'd expect from advanced image editors, and the latest version has added new effects (including new blurs and distortions), better performance, and a complete refresh of the user interface.
The latest version is Paint.NET 3.5 and is available in English, Chinese (Simplified), French, German, Italian, Japanese, Portuguese (Brazil), Russian, and Spanish.
If you need to do the occasional image tweaking or heavy image editing but don't want to spend a lot of cash on Photoshop or dive into GIMP, Paint.NET is well worth the download. It may not be able to do everything Photoshop does, but it can do everything most users need. Paint.NET for Windows is a free application although the authors do accept donations. Paint.NET is available at http://www.getpaint.net.