The SpyderCheckr Color Calibration Tool for Digital Cameras from Datacolor is a color target for use with digital cameras. It features 48 swatches, including various shades of gray and skintones. You can use the swatches to perform a custom white balance on your camera, ensuring that your camera settings correctly match the lighting conditions in which you are shooting.
The SpyderCheckr ships with software for Mac and Windows. In order to use it, you'll have to use an Adobe Camera RAW (ACR) post-production workflow. This allows you to use the calibration tool in conjunction with Photoshop, Photoshop Elements, and Photoshop Lightroom.