Auto Crop is a Script UI tool for After Effects that will rezise a composition to fit its contents. Auto crop give you three ways to crop your composition. 'Auto Crop' will crop you composition at the current frame. 'Auto Crop Duration' will examine each frame of your composition and crop based on the entire length. That way even if you have animation inside, you can crop without cutting anything out. You can also 'Crop to Mask' wich allows to crop based on a mask you have created.
This crop will work on anything that has alpha, which means you can crop compositons containing anything from simple solids to particles.
Auto Crop is still in beta, so if you notice any issues, please leave a comment and let me know.
After Effects CS3 or higher is required.