Photoshop CS Studio Techniques is one of the clearest software books I've ever read - Ben Willmore cuts through all the techno-speak without ever being patronising.
The book is printed in full colour, and almost every page has complete photographic examples and screenshots. The accompanying CD also contains a bunch of the stock images used so that you can follow through the given examples, although you'll probably end up experimenting with the tools rather than following Ben's exact steps.
Ben concentrates on highlighting the reasons behind each function, filter and tool in Photoshop CS, and at the end you feel like you actually understand what you're doing rather than just carrying out a series of steps you've been taught.
The book is focused on practical Photoshop uses and doesn't spend time beating around the bush on fancy techniques you'll never use (although many of the more esoteric features of Photoshop are at least touched upon). If you're looking for something that tells you how to actually use Photoshop but isn't written like a software manual or a series of school lessons, this is the perfect book.
The target audience for this book is probably anywhere from beginner to the upper end of intermediate. Ben assumes that you've managed to work out how to install the software, but beyond that you're taken step-by-step through everything. Advanced users will probably find some of the early chapters a little basic, but should still get a lot out of the practical examples and may well learn how to streamline their workflow better.
For a thorough grounding in understanding Photoshop CS, starting at the beginning, you probably can't do much better than this.