I've been reading The Subterranean Railway over the weekend, an excellent history of the London Underground. It's written in an entertaining way, with some great nuggets of information (such as the tube's original no smoking policy being overturned by an amendment to the Railway Regulation Bill requiring all railways to provide a smoking car).
What's interesting is that by looking at the history of how the tube was created, you begin to understand a lot of the strange quirks of the system today. Decisions made back then still affect today's commuters on a daily basis.
There's a lot of descriptions taken from source material about what it was like riding the tube back then (with steam engines, poor ventilation and all), and suprisingly there are a lot of parallels with travelling on the tube today. I was amused by a photo of a tube train carrying a sign reading 'allow passengers to alight first please'.
It's a great book and I recommend it for anyone who lives in London and takes the tube. My copy is signed by the author, Christian Wolmar, who also wrote Going Down the Tube - an account of why PPP is such bad news...