A humorous book to read before skipping across the pond is "Notes From A Small Island" by Bill Bryson. Bryson, an American, gives his impressions and insights into British culture as he completes a whirlwind tour before moving back to the U.S.  This book is a great read for the plane (but bring another book because this one goes quickly) - though if you have a tendency to laugh out loud you might not make yourself too popular!

For a slightly deeper insight into the English, "Watching the English" by Kate Fox also makes a good read. Fox, a social anthropologist by trade, examines the English from a professional point of view and tries to work out the rules that govern English behaviour. Of course, being English herself, she is unable to do so without a liberal sprinkling of humour, and the book is well written. English people will read it and squirm ("Yes, ..do that!"), foreigners will hopefully start to understand a little of what makes the English tick.

Great Britain, by Eyewitness Travel Guides (published annually), is an excellent comprehensive general guide.

Also Rough Guide, Time Out and Let's Go series. 

Small Island, by Andrea Levy (2005) provides an insightful account of the wave of Jamaican immigrants that came to the UK after World War II.

A Sense of the World:  How a Blind Man Became History's Greatest Traveler (published in 2006) is an outstanding biography of James Holman, a sightless Brit who managed to fight the slave trade in Africa, travel across Siberia, and hunt Elephants in Ceylon among other amazing accomplishments.