i.Mage is a small and fast graphics editor slanted towards quite and easy pixel editing, ala DPaint from the DOS/Amiga days. Instead of being a bloated behemoth with a zillion plugins it starts in under a second and it does a lot of the mundane jobs of image editing quickly and without fuss. The right tool for simple jobs.
Source code is available under the LGPL.
Download: i.Mage 1.09