Second for Foyles. Although it is these days a fairly standard chain bookstore it is such an important historical building: the literary luncheons that played such a key role in the Bloomsbury set, the queues round the block to buy DH Lawrence before the ban came down etc...

Although it has to be said the thing Foyles was mostly famous for was what an incredibly bad bookshop it was to the 1950s to the 1980s where, under the management of the eccentric Christina Foyle who loathed her staff so much she refused to allow them to handle money, you could only buy a book through an exasperating triple queue system (order, invoice, collect), books were only sorted by publisher and date of publication, and acquisition choices were eccentric in the extreme (making it a great place to stumble across a rare book by accident but a terrible place to find anything you were looking for). It's now much much more normal, but what's the point in that? Would you buy soup from the soup nazi if he was nice now?