Northumberland House (1752) by Canaletto
Halley Docherty (Reddit user shystone) has created 10 mashups of old paintings of London and placing them in their modern settings. I think you'll agree that the juxtapositions created are stunning.
A View of Greenwich from the River (1750-2) by Canaletto
Blackman Street London (1885) by John Atkinson Grimshaw
Covent Garden Market (1737) by Balthazar Nebot
St Martins in the Fields (1888) by William Logsdail
The 9th of November, 1888 (1890) by William Logsdail
The River Thames with St. Paul's Cathedral on Lord Mayor's Day (1746) by Canaletto
The Strand Looking East from Exeter Exchange (1822) Artist Unknown
View of The Grand Walk (1751) by Canaletto
Westminster Abbey with a Procession of Knights of the Bath (1749) by Canaletto
You can learn more about each image on the imgur album page.