There are small museums which were simply the personal collection of one wealthy person, such as the Sir John Soane Museum, and the Hunterian Museum, which holds a very interesting medical collection within the Royal College of Surgeons (where I worked for a few months). I will shortly be writing a further web page on London, indeed a series in time for visitors to check out before the 2012 Olympic Games. So look out for more of the same.
I have also been wondering whether there would be any call for people wanting to rent a room with a family in London for a few days during the Games - I know lots of Londoners who would be happy to oblige, if you don't mind being in a suburb a little way from the centre, with something a lot less than luxury, but homely and welcoming nonetheless. Let me know if you think I should maybe do a short web page about that.