The Unofficial Guide to Washington, DC offers comprehensive information in a clear, concise style. There is plenty of basic information about how to get around in the city using the Metro, what time of year to go, how to stay safe, etc. In addition, you will find hotel ratings and detailed entries on all major attractions inside the city. The hotel section is probably the weak point of the guide. It offers a numerical rating system but only a few basic items of information on the hotel. There is no written description with the pros and cons of each hotel spelled out for you.
The section on attractions is where this guide makes up for the lack of hotel info. It covers all the museums, memorials, monuments, government buildings, etc. Each entry is highly detailed with full contact information, nearest Metro stop, tips on when to go, full descriptions, touring tips, and other things to do nearby. It is literally everything you want to know when considering a visit to one of the many tourist attractions in the city.
While planning my trip to Washington, DC I bought three guidebooks to the area. This is the only one that I used in the latter stages of planning and also the only one I used when I got to the city. It was easily the most comprehensive and useful of the lot once I had booked my hotel. If you're planning a trip to the capitol and can only buy one guide, get this one.