The first travel guide I always pick up right after I book a trip is a Wallpaper* City Guide. They are a steal at $11.95 each and produced by the Editors of the ultra-hip Wallpaper* Magazine. These mini pocket books are a great starting point for prioritizing cool architectural sites, mod hotels, stores, spas, day trips, restaurants and bars. It cuts through all the usual travel guide fluff and I use them to supplement a bigger guide book from Lonely Planet or Frommers. You also get lots of full-colour photos for each recommendation.
Over 80 city guides are now published by Phaidon. 10 cities are available via an iPhone app for $5 via iTunes. Pick one up for your next trip and get down to business when you don't have the time to read a 400-page guide book. You can find the Wallpaper* City Guides online on Amazon.