Wallpaper* City Guide: London 2008
Phaidon has a great series of city guides. I used the Cairo one on my trip and it was fantastic for restaurant recommendations and for giving a different perspective on the architecture, art and culture of the place.
I highly recommend these as supplemental guides. Not a great replacement for your full-blown guide book, but definitely necessary reading in advance of the trip, good for nightlife planning, and perfect as small, pocket-sized gems that you can easily cart around while on tour.
A full range of stars for these city guides.