A small sprite combiner written in shell. Used on: http://opengameart.org/content/700-sprites

gistfile1.txt

#!/bin/sh

for f in *.gif
do
	short=${f:0:4}
	if ls $short".png" &> /dev/null; then
		echo "file exists"
	else
		montage -tile x1 -geometry +0+0 -background none $short*.gif $short.png
		convert $short.png -transparent white $short.png
	fi
done

You can take it one step further and build it into a single texture (using the 256x32 pngs):
montage -tile 4x -geometry +0+0 -background none *.png ../lastguardian-all.png

That will create a 1024x736 png with all the sprites. I put up a copy here:
http://postimg.org/image/mqncja9q9/

Remember to credit him:
... Philipp Lenssen and my website is outer-court.com . An appropriate link to the site and credit by name would be appreciated in your projects.