For those new to the DK Eyewitness books I cannot recommend them highly enough for their clear guide content, pictures, diagrams and information. I have found that it replaces the need to buy a guide book in many attractions (eg Westminster Abbey) as there is sufficient info contained to satisfy most travellers' interests. The guide is broken down neatly into regions with basic maps which makes it easy to use when on a driving holiday or planning your day's itinerary. On the downside, the 672 glossy pages, though beautiful, get very heavy in your backpack etc when you are on your feet all day.
In summary, I love these guides and search for them first when visiting anywhere new.
A final note to answer another's review, there are separate guides for Scotland, Ireland, London etc that cover those areas in more detail.