Don't crop. Use Photoshop's Trim feature.
Sometimes after working with images on a transparent background, you're left with extra space around your object. Cropping the image precisely can be tricky, especially if you have soft shadow edges.
This is where Photoshop’s Trim command comes in so handy (choose Image > Trim in Photoshop's menu).
As long as the area you want to crop is transparent or a solid color, the Trim dialog box lets you instantly crop your document's canvas to the outer border of your image.
While this feature has been part of Photoshop from the very early years, a lot of designers miss it along the way. A great time saver.
Source: We use Photoshop’s Trim command all the time while preparing screen shots for these weekly tips. This is the feature that attracts the most comments from people who happen to be watching over my shoulder. For this tip, I borrowed some wording from the Creative Guy archives.