If you have internet while traveling to London, you should get this free amazing iPhone Web App. It even has audio commentary. If not I recommend getting this London Audio Guide.
This turns your iPhone or iPod touch into your own personal tour guide, including full audio commentary. The guide will help you plan your trip to London by showing you what to see and do, including opening times, entry prices and plenty of photographs. The guide then helps you make the most of your visit by telling you entertaining stories …