piCSSel-art - Draw pixel art with CSS!
Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Pixel Art Studio - A purpose-built drawing tool for pixel artists
Pixilart - A drawing app for delightfully retro pixel art
Juice FX - Easily turn your pixel art into VFX for your video game.
Piskel - Piskel is a website where designers online create sprites or pixel art.