Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Grafx2 - GrafX2 is a bitmap paint program inspired by the Amiga programs Deluxe Paint and Brilliance.
IconLover - Icon editor for Windows.
LibreSprite - Free and open source program to create animated sprites.
Piskel - Piskel is a website where designers online create sprites or pixel art.
Lospec Pixel Editor - Free online pixel art program. It's easy to use, intuitive and unobtrusive.