An interesting article about Blake from The Guardian 4 March 2007
The invisible worm
London from Wikipedia
A complete analysis of the poem from BBC Bitesize
A very good lecture which thows light on every possible feature in the poem
A detailed stylistic analysis of London
A fine site featuring a few interesting lectures on London: Dr. Jonas Prida on William Blake's 'London'
An article with a slightly different view on William Blake's London
William Blake's London at the Norton Antology of Poetry