Sprite Cow - Generate CSS For Sprite Sheets
Automated spritesheet generators are pretty cool, but I prefer the control over optimisation and compression you get by making them manually. However, copying all the positions & sizes from graphics apps will wasted a ton of your time.
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