My wife and I just returned from a trip to Prague and Budapest a month ago (using Rick's guidebooks to plan the trip) and upon returning I read two books that complimented our trip very well. I think both are better to read AFTER your trip, as it really helps to have been in those cities and to have walked around the major streets and sites to fully appreciate the books.
One is Prague in Black and Gold and the other is Budapest: Portrait of a City Between East and West. The latter just came out this year and is the better written of the two.
Reading each of them provided additional facts about these two lovely cities and helped me relive some new memories of our recent trip.