I'll throw the old version of
Aseprite into the mix. The latest versions are paid software, but 0.9.5 is extremely usable and unlike the free version of Graphics Gale, it has GIF support.
Edit: Forgot my standard warning. Aseprite scales pixels to 200% instead of 100% by default. To fix this, you have to change a single value in the .ini file found in the program's folder.
Close the program (if it's open) and change
ScreenScale = 2
to
ScreenScale = 1
Then relaunch the program.