Sprite Monkey is a sprite sheet maker. It converts your png images into a sprite sheet or strip. Just select a folder of png images and then select what you want to save it as. Also, has an option to change the colors from 32-bit to 24, 8, 4, 1-bit with optional dithering. Or even exporting the alpha channel for the use of special effects like shadows and masking!
Sprite Monkey currently works best for those who create games using the power of 2. Which is the fastest way for a video card to render the graphics!