Paint.NET - Paint.NET is a free image and photo editing software.
PhotoFlare - Quick, simple but powerful Cross Platform image editor.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
KolourPaint - KolourPaint is a free, easy-to-use paint program for KDE (a desktop environment for UNIX).
showFoto - ShowFoto is the standalone image editor of the digiKam project.