The Royal Society of Arts was the first body to act on a suggestion that commemorative plaques be erected at the homes of famous London inhabitants; its first plaque was erected in 1867 at the birthplace in Holles Street, London (since demolished) of Lord Byron, the Romantic poet. By 1901, when the London County Council took over the scheme, 36 plaques had gone up -- when in turn it was handed over to the Greater London Council in 1965, 298 were in place. The GLC extended coverage outside "London" proper, and the current body, English Heritage, took the reins in 1986. So far as London is concerned, there are now about 800 plaques -- the oldest surviving being those to poet John Dryden (Gerrard Street in Chinatown) and to Emperor Napoleon III (King Street St James'), both erected in 1875.
So you'll know what to look out for and what colour means what date: the first plaque was deep blue with white lettering; most of those erected before 1900 are chocolate-brown; 1903-21, the LCC used stone/metal and glazed terracotta and, in 1921, glazed Doulton-ware became standard. A plainer design was adopted in 1937, with the white border added in 1939. Most plaques are a 19"-diameter, circular blue/white design of glazed earthenware (though special designs in other materials are occasionally used). Each identifies the individual commemorated, plus what they did there (usually "lived here") and when they did it, or what specific event happened at that place. Some of the fun comes from the bizarre descriptions given to people or events - my favourite is Luke Howard (1772-1864) - commemorated as "namer of clouds" at 7 Bruce Grove Tottenham N17. But there's something for almost every nation and interest group.
Other favourites (and details of where you can find them - in my own categories) are...
1 POLITICIANS, REVOLUTIONARIES AND ROYALTY
1.1 Mahatma GANDHI (1869-1948) - philosopher and teacher - stayed here in 1931. Kingsley Hall Powis Rd E3
1.2 William WILBERFORCE (1759-1833) - resided here during his campaign against slavery, successfully conducted in Parliament. 111 Broomwood Rd SW11
1.3 CHARLES X (1757-1836) - last Bourbon King of France. 72 South Audley St W1
1.4 Maharlal NEHRU (1889-1964) - first Indian Prime Minister. 60 Elgin Crescent W11
1.5 Karl MARX (1818-83) 28 Dean St W1
1.6 Benjamin FRANKLIN (1706-90) - US statesman and scientist. 36 Craven St WC2
1.7 Bertrand RUSSELL (1872-1970) - philosopher and "campaigner for peace." 34 Russell Chambers Bury Place WC1
1.8 Simon BOLIVAR(1783-1830) - liberator of Latin America. 4 Duke St W1
1.9 Nancy ASTOR (1879-1964) - first woman to sit in Parliament. 4 St James' Sq SW1
1.10 Andres BELLO (1781-1865) - poet, jurist, philologist and Venezuelan patriot. 58 Grafton Way W1
1.11 Prince Peter KROPOTKIN (1842-1921) - "theorist of anarchism". 6 Crescent Rd Bromley
1.12 Sir Winston CHURCHILL KG (1874-1965) - Prime Minister - lived and died here. 28 Hyde Park Gate Kensington Gore SW7
1.13 General Charles de GAULLE - President of the French National Committee, set up Free French Forces HQ here in 1940. 4 Carlton Gardens SW1
2 HEROES
2.1 Violett SZABO GC (1921-45) - secret agent who gave her life for the French Resistance. 18 Burley Road Stockwell SW9
2.2 Horatio Lord NELSON (1758-1805). 147 New Bond St W1
3 MISCELLANY
3.1 Madame Marie TUSSAUD (1761-1850) - "artist in wax." 24 Wellington Rd St John's Wood NW8
3.2 Mary HUGHES (1860-1941) - "friend of all in need." 71 Vallance Rad E2
3.3 Robert BADEN-POWELL (1857-1941) - "Chief Scout of the World." 9 Hyde Park Gate SW7
3.4 Beau BRUMMELL (1778-1840) - "leader of fashion." 4 Chesterfield St Mayfair W1
3.5 William BLIGH (1754-1817) - Commander of the "Bounty." 100 Lambeth Rd SE1
3.6 William LEVER, 1st Viscount Leverhulme (1851-1925) - "soap-maker and philanthropist." Inverforth House North End Way NW3
4 ARTISTS
4.1 Antonio (Canaletto) CANAL (1697-1768) - Venetian painter. 41 Beak St W1
4.2 Vincent van GOGH (1853-90). 87 Hackford Road SW9
5 EXPLORERS
5.1 T.E. LAWRENCE ("Lawrence of Arabia") (1888-1935). 14 Barton St SW1
5.2 Howard CARTER (1874-1939) - Egyptologist and discoverer of the tomb of Tutankhamun. 19 Collingham Gardens SW5
5.3 Captain Robert Falcon SCOTT (1868-1912) - Antarctic explorer. 56 Oakley St SW3
5.4 Captain James COOK (1728-79) - circumnavigator and explorer. 88 Mile End Rd E1
5.5 Charles DARWIN (1809-82) - naturalist. Biological Sciences Building University College Gower St WC1
6 LOCATIONS
6.1 TELEVISION - world's first regular high definition television service inaugurated here by the BBC 11.1936 Alexandra Palace Wood Green N22
6.2 FLYING BOMB - first Flying Bomb on London fell here 13.6.1944. Railway Bridge Grove Rd Bow E3.
6.3 MILLBANK PRISON - opened 1816/closed 1890. Buttress stood at the head of river steps from which, until 1867, prisoners sentenced to transportation embarked on journeys to Australia. Millbank SW1
7 COMPOSERS AND MUSICIANS
7.1 Frederic CHOPIN (1810-49) - left this house in 1848 for the Guildhall to give his last public performance. 4 St James' Place SW1
7.2 Jimi HENDRIX (1942-70) - guitarist and songwriter. 23 Brook St Mayfair
7.3 Wolfgang Amadeus MOZART (1756-91) - composed first symphony here in 1764. 180 Ebury St SW1
8 WRITERS
8.1 Percy Bysshe SHELLEY (1792-1822) - poet. 15 Poland St W1
8.2 Bram STOKER (1847-1912) - author of "Dracula". 18 St Leonard's Terrace SW3
8.3 Ian FLEMING (1908-64) - creator of James Bond. 22 Ebury St SW1
8.4 John KEATS (1795-1821) - poet. Wentworth Place Keats Grove Hampstead NW3
8.5 Washington IRVING (1783-1859) - American writer. 8 Argyll St W1
8.6 Siegfried SASSOON (1886-1967) - poet. 23 Campden Hill Sq Kensington W8
8.7 Dorothy L SAYERS (1893-1957) - writer of detective stories. 24 Great James St WC1
8.8 Henry JAMES (1843-1916) - American novellist. 34 De Vere Gardens W8
8.9 David Herbert LAWRENCE (1885-1930) - novelist and poet. 1 Byron Villas Vale of Health Hampstead NW3
8.10 Rudyard KIPLING (1865-1936) - poet and story writer. 43 Villiers St WC2
8.11 Oscar O'Flahertie Wills WILDE (1854-1900) - wit and dramatist. 34 Tite St SW3
8.12 A.A. MILNE (1882-1956) - creator of "Winnie the Pooh". 13 Mallord St SW3
8.13 Dylan THOMAS (1914-53) - Welsh poet. 54 Delancey St WC1
8.14 Sir Arthur Conan DOYLE (1859-1930) - creator of Sherlock Holmes. 12 Tennison Rd South Norwood SE25
8.15 Alfred Lord TENNYSON (1809-92) - poet. 9 Upper Belgrave St W1
8.16 Joseph CONRAD (1857-1924) - novelist. 17 Gillingham St SW1
8.17 Dame Agatha CHRISTIE (1890-1976) - detective novelist and playwright. 58 Sheffield Terrace W8
8.18 George ORWELL (1903-50) - novelist and political essayist. 50 Lawford Rd NW5
8.19 H.G. WELLS (1866-1946). 13 Hanover Terrace NW1
8.20 Sir Noel COWARD (1899-1973) actor, playwright and songwriter - born here. 131 Waldegrave Rd Teddington
8.21 Daniel DEFOE (1661-1731) - novelist. 95 Stoke Newington Church St N16
8.22 Samuel PEPYS (1633-1703) - diarist and Secretary of the Admiralty. 12 Buckingham St WC2
8.23 Mark (Samuel Langhorne Clemens) TWAIN (1835-1910) - American writer. 23 Tedworth Sq SW3
8.24 Charles DICKENS (1812-70) - novelist. 48 Doughty St WC1 [see other entry for Dickens above]
9 PERFORMERS
9.1 Paul ROBESON (1898-1976) - singer and actor. The Chestnuts Branch Hill NW3
9.2 Boris KARLOFF (alias for William Henry Pratt) (1887-1969) - actor - born here. 36 Forest Hill Rd East Dulwich SE22
9.3 Sir Alfred HITCHCOCK (1899-1980) - film director. 153 Cromwell Rd SW5
9.4 Vivien LEIGH (1913-67) - actress. 54 Eaton Sq SW1
10 INVENTORS AND SCIENTISTS
10.1 Sir Ronald ROSS (1857-1932) - Nobel Laureate; discoverer of the mosquito transmission of malaria. 18 Cavendish Sq W1
10.2 John Logie BAIRD (1888-1946) - first demonstrated TV here in 1926. 22 Frith St W1
10.3 Sir Geoffrey de HAVILLAND (1882-1965) - aircraft designer. 32 Baron's Court Rd W14
10.4 Michael FARADAY (1791-1867) - man of science - apprenticed here. 48 Blandford St W1
10.5 Alan TURING (1912-54) - code-breaker and pioneer of computer science - born here. 2 Warrington Cresent Maida Vale W9
10.6 Sigmund FREUD (1856-1939) - founder of psychoanalysis. 20 Maresfield Gardens NW3
10.7 Aldous HUXLEY (1894-1963) - man of science and letters. 16 Bracknell Gardens Hampstead NW3
10.8 Samuel MORSE (1791-1872) - American painter and inventor of the Morse Code. 141 Cleveland St W1