For information on the area around the Medway Towns, have a look at Medway Council's CityArk site.
Ordnance Survey Maps of England and Wales - Revised: Kent illustrates the parish boundaries of Kent when rural districts were still in existence and before Greater London came into being. The map publication year is 1931. An earlier map of 1900 may also be useful. The maps blow up to show all the parishes and many of the small villages and hamlets. Maps in this series are now downloadable for personal use.
Census records for Kent are available on FamilySearch, Ancestry and FindMyPast. The first site is free; the other two are pay sites but have access to microfilmed images. Steve Archer produced a very useful round-up of the available sources, but this information may not be up to date.
Registration Districts in Kent for the period 1837 to the present. By drilling down through the links you can follow any parish through the registration districts to which it was attached.
Woolwich & District FHS (serves eastern sections of Greater London which were in Kent until 1966)
Volume 2 of the Victoria County History of Kent (published 1926) is available online through the auspices of British History Online. It includes accounts of the early history of Canterbury and Rochester cathedrals, and of several sites now within the conurbation of London.
Volume 3 of the Victoria County History of Kent (published 1932) This includes the text of, and the index to, the Kent Domesday survey. It has been provided by the Kent Archaeological Society.
In place of the other volumes of the Victoria County History, British History Online has transcriptions of the numerous volumes of The History and Topographical Survey of the County of Kent by Edward Hasted (originally published 1797)
English Jurisdictions 1851, a parish finding aid provided by FamilySearch, is particularly helpful in locating parishes in large ancient towns and cities like Canterbury.