I've been playing around with spritesheets quite a lot recently. During my experiments I used a lot of prexisting spritesheets such as those from the Metal Slug games . Creating animations out of those spritesheets was tedious though as I had to manually mark every sprite's coordinates because each sprite wasn't the same size. And even if all the sprites were the same size, creating animations out of them still took a bit of work. To help with this I created a simple AIR app that allows you to easily create and edit animations from a given spritesheet. 

Once the animations have been marked up you can export the data and import it into your own application to be used. These lets you easily access animations by name.