Last week I was somewhat disappointed, as I was half-way through reading it, to sell our only copy of Nicholas Barton's The lost rivers of London, a fascinating book that started out as a PhD thesis. Barton documents the history of rivers such as the Fleet and Walbrooke; although long since piped and buried, they still remain an influence on placenames, surface features and underground planning.
There's a nice map at The Open Guide to London Lost Rivers page, and a good overview at Barryoneoff's Rivers that disappeared. This defunct Heritage Magazine article, The Underground City, with topological map, gives more context on how the main rivers interact with other features. London Geezer's series of blog posts, Reviewing the Fleet is a superb study of the complex history of the River Fleet (now a sewer).
For anyone with an interest in London of the past, Henry Mayhew's 1851 London Labour and the London Poor is more or less required reading. A three-volume compilation of an article series Mayhew wrote for the Morning Chronicle, it combines scholarly research with sympathetic interviews of a broad spectrum of people at the lower end of London's social scale. The account of Jack Black, " rat and mole destroyer to Her Majesty", gives an idea of the flavour.
The Bolles Collection on the History of London has a full searchable text: for instance, accounts of the sham indecent trade (a con involving the sale of sealed packages of allegedly pornographic material, that turn out to contain rubbish); snail-sellers; death hunters (who sold false news of celebrity accidents); a depressed street clown; 'pure' finders (dog dung collectors); 'screevers' (who wrote begging letters for others); disaster beggars; and more. The full text is heavy going, especially to read online, but there are many selective editions about, such as a Penguin paperback. If you do want to tackle the full version, the first three volumes are the most interesting; the fourth 'Extra Volume' on prostitutes, beggars and thieves is mostly written by co-authors and (maybe out of coyness and/or legality) departs from Mayhew's detailed interview format in favour of lengthy dissertation and statistics.
A third book recommendation for Londonophiles: Ronald Wright's A Scientific Romance. A book that rather fell between genres - literary and SF - this uses the vehicle of the HG Wells Time Machine to take the narrator, the archaeologist David Lambert, to the year 2500. If for nothing else, this book is worth reading for its stunning descriptions of Lambert's exploration of overgrown tropical London - one of a long history of apocalyptic visions of that city (see Where London Stood). - Ray