Ancestry.co.uk Censuses from 1841 to 1911, Births Marriages and deaths index, plus many other features. Subscription, but excellent value. Other useful databases that I have found are Wills, Probate Calendars, Phone Books, Ship's registers and Passenger lists and many many more. Of the main geneaology sites has in my opinion (and others according to many web forums) by far the best user interface.
cityark.medway.gov.uk The web presence of the Medway Council Archives. Searchable database of piece-level descriptions of original historical archival documents, and imagebase of scanned images of the most popular records, including most parish registers. The individual images are not indexed but you can often find a reference on other sites. Completely free.
nationalarchives.gov.uk A wealth of information about the National Archives. Much information is available online - for example wills and military records can be downloaded for a small fee..
nwkfhs.org.uk Society for the study of family history, genealogy and heraldry in South East London and North West Kent. Many useful publications, including CDs of parish registers
GenesReunited.co.uk Contact others with common ancestral interests. Subscription required to contact. I found it useful in the past but changes they made a couple of years ago have rendered it pretty useless so I have cancelled my subscription.
familysearch.org "The largest collection of free family history, family tree and genealogy records in the world". Compiled by The Church of Jesus Christ of Later Day Saints, but as people can upload directly to the site some of it may be misleading. Nevertheless can be extremely useful for locating individuals before 1837.
findmypast.co.uk Full Births, Marriages and Deaths indexes, plus census.Now has 1921 census. Beware though a subscription does not give access to this - currently only available as par-per-view.
realestateagents.com/articles/house-history-genealogy Site about house history and genealogy. (Thanks to Elijah for this suggestion)
Levy Family Southampton UK Website of Chris Levy, descendant of James Barham, through Richard and Gertrude.
mandywillard.co.uk/surnames/barham/family.htm Barham family group pages on the website of Mandy Willard. Extensive site with many other names
londonlives.org A fully searchable edition of 240,000 manuscripts from eight archives and fifteen datasets, giving access to 3.35 million names.
coadb.com/surnames/barham-arms.html . Aims to be the worlds largest online heraldry database. Currently has 9,500 arms. Each page also contains the blazons. All of arms are fully sourced to real historical documents. The main sources used are Burke’s Armorial Général, authored by Sir Bernard Burke and published in 1884, as well as the Armorial General, authored by Johannes Baptista Rietstap in 1861.
familycrestdb.com/barham.html A website where you can purchase the Barham coat of arms (and many others) on t-shirts, mugs, posters, and over 40 different gift items.