Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Pixel Studio - The Pixel Art Is Always Fun
Pixel Art to CSS - Draw and animate pixel art, export the results to CSS
Piskel - Piskel is a website where designers online create sprites or pixel art.
piCSSel-art - Draw pixel art with CSS!
Pixilart - A drawing app for delightfully retro pixel art