sprite cow helps you get the background-position

sprite cow helps you get the background-position, width and height of sprites within a spritesheet as a nice bit of copyable css. I personally found it pretty useful and easy to use.
There are one or two rather clever tricks happening with Javascript and Canvas to discover the dimensions of images and generate the CSS, they have also shared the code on Github so that others can see under the hood.

Requirements: -
Demo: http://www.spritecow.com/
License: MIT, GPL License sprite cow