This may be slightly off the topic of London maps, but there's an excellent new Google Map on the website for the current BL exhibition, Sacred: Discover what we share. Definitely worth a look..
Although the exhibition London: A Life in Maps has closed some time ago, don't forget that you can still experience it online - where it will remain for the forseeable future at least - so you can still take a look at London as you've never seen it before!
Just a quick note to let you know about a fantastic new Google Earth layer based on London: A Life in Maps that a colleague in our web team has put together. You can download about 10 maps from the exhibition & view them as image overlays in Google Earth