Sprite Cow is another one which is open source and works very effective by auto-recognizing the different elements inside a single image.
So, you design the sprite image in your favorite imaged editing application, upload it to Sprite Cow and simply click (or click + drag) on each element to get their width, height and background-position as a CSS rule.
Sprite Cow is web based tools helps you get the background-position, width and height of sprites within a spritesheet as a nice bit of copyable css. The source code also available for download on github.
Website: http://www.spritecow.com/
Download: https://github.com/jakearchibald/sprite-cow
