Lonely Planet Washington, DC & the Capital Region: Travel Survival Kit

This is one of the most complete guides to the region that I have ever seen, and I've lived in all the states covered (including Washington, DC) except for Delaware. There are some holes--northeastern Maryland is not covered at all nor is part of Virginia's Allegheny Highlands--and the book now suffers from Lonely Planet's practice of not updating their guides annually, but for in-depth coverage of off the beaten track areas such as western Maryland and southwest Virginia, where I live, this book is superior to any other guide I've ever seen.