LodePaint is a painting program aimed at pixel art, sprites, textures, photo editing, HDR image editing and computer graphics effects.
*) Many tools and filters
*) Easy navigation: arrow keys move cursor, zooming while using tools, etc...
*) Focused on pixel editing, textures and sprites
*) Create and edit High Dynamic Range images
*) Easy editing of the alpha channel
Do filters on multiple images at once
*) PNG, JPEG, GIF, TGA, BMP, RGBE, OpenEXR (on linux only), DNG import