On a recent trip to Berlin this book never left my side. It's small enough to fit into a handbag or fanny pack, and it will guide you through Berlin just as well as any tour guide.
Lonely Planet Berlin has more information than you'll probably need and it's more up-to-date than any of the other guidebooks out there. I've read Frommer's and Fodor's and they don't compare to Lonely Planet. I also prefer this book to the Michelin Guide books. If you don't like to read guide books and prefer to show up and see-what-happens, than you'll want to buy this book for the detailed maps in the back. There are eight different maps covering different sections of Berlin. Each map gives you the exact locations of numerous Places to Stay, Places to Eat, Places to Drink and Other: museums, points of history/ interest, police stations, post offices, etc. There is also a detailed map of Berlin's rail lines.
The author, Andrea Schulte-Peevers, wrote the 1998 edition with her husband David Peevers and they certainly are the experts of where-to-go and what-to-do in Berlin. Trust me, this book is a must for anyone wanting to visit this amazing city!