If you have a digital camera, you need Adobe Photoshop to get the best from it.
But if (like me) you can't afford the full version of Photoshop, Adobe's Photoshop Elements is the next best thing.
And if you use Photoshop Elements, then you should look at this book. It will definitely change the way you think and use Photoshop.
Scott Kelby and Matt Kloskowski provide a comprehensive how to guide which unapologetically does not waste space covering the basics of digital photography (as covered in too many other books). Instead it starts from the assumption that the photograph is taken, and that your mission is to turn that photograph into a masterpiece. It provides straightforward and easy-to-follow instructions on how to correct and crop your photographs, perform digital darkroom techniques such as dodging and burning, fix colors and flesh tones, remove blemishes, compensate for distortion and vignetting, and so on.
Adobe's online help files and tutorials were good, but they really didn't help me figure out all the things I could do with Photoshop Elements. This book has saved me countless hours and helped me get the best out of the product.
(These books get updated with every version of Photoshop Elements - they don't change much so if you don't mind slightly out-of-date screenshots, getting one for a previous version is significantly cheaper.)
(Click on the image for more information about this book.)