Abney Park Cemetery
The final resting place of London's Non-Conformists.
http://www.abney-park.org.uk/

BBC.co.uk
A guide to a group of particularly noteworthy London cemeteries which are collectively known as the "Magnificent Seven".
http://www.bbc.co.uk/london/yourlondon/unitedcolours/cemeteries/index.shtml

Highgate Cemetery
The cemetery includes Karl Marx's grave, among others.
http://www.highgate-cemetery.org/

Kensal Green Cemetery
The last resting place of Isambard Kingdom Brunel and William Thackeray.
http://www.kensalgreen.co.uk/