Those with London ancestors will relish the latest new archive on Ancestry.co.uk: Electoral Registers for London for the period 1835-1965.
These registers list the names of all those eligible to vote in elections. The right to vote at first did not cover everyone. Property ownership prevented access to the vote for the lower classes. Women were also excluded. It was not until 1928 that all men and women over the age of 21 were allowed to vote. For more information on whether your ancestor may have held the right to vote, see this useful London Metropolitan Archives fact sheet.
The registers can be searched by name and it is possible with the aid of a map to drill down to a particular address.