London Remembers has mapped over 2,000 memorials in London. Their website includes a Google Map showing the locations of plaques, monuments, statues and fountains throughout the capital.
Each mapped memorial includes a couple of photographs of the memorial. If you click the link in the marker you can view more details about who (or what) is being memorialised. If you don't want to browse London Remembers by location you can also search the database by name, category and date.