Using Automator to batch crop with custom coordinates / measurements

I'm trying to crop large batches of images automatically. I'm currently using Automator's Crop Images action, but it is lacking in options. I can specify a width and height, and then it performs a centered crop. I want to be able to specify X and Y as well as width and height (to use Xcode terms), so I can perform a consistent crop for any custom rectangle. Are there better, more featureful cropping actions available? Preferably for free... :)