Don't know about you, but when I travel I love to fit my reading to the place I'm visiting.
If you're off to London any time soon (one or two of you are there already!), you might enjoy this guide to the city in books, produced by Booktrust for the Get London Reading campaign. (The full, interactive map features 400 books set in, or about the capital, and if you find that any books have been forgotten - you can just add them!)
Of course Dickens and Conan Doyle are necessary choices, but there are plenty of suggestions for contemporary fiction including Sarah Waters The Night Watch, Zadie Smith's White Teeth, and Gautam Malkani's Londonstani.