Greater London on Wikipedia.

My knowledge of the divisions of London are very vague. If a church is wrongly listed here, please let me know!!

The City of London

The City of London on Wikipedia.

Churches marked † are (in part at least) by Wren. Again, any corrections would be welcome.

All Hallows-by-the-Tower, Barking, Byward St. From an old postcard, Bulman Collection. A modern view. © Mark Summers. Another view. © Andrew Ross. And another © Peter Morgan. TQ 333 806. Link.
All Hallows, London Wall. © Aidan Thomson. Interior view. © Carole Sarvis. Link.
All Hallows Staining, Mark Lane. Only the tower remains, the rest of the church was demolished in 1870. © Mark Summers. Link.

Chapel Royal of St. Peter ad Vincula (the chapel of the Tower of London). © Peter Morgan. Link.
Christ Church, Spitalfields. © Aidan Thomson. Link.

Dutch Church, Austin Friars. Interior view. Both © Aidan Thomson.

St. Alban the Martyr, Holborn. © Aidan Thomson. Link.
St. Alban†, Wood St., a victim of WW2, only the tower remains. © Aidan Thomson. Link.
St. Andrew Undershaft. © Mark Summers. Link.
St. Anne & St. Agnes†, Gresham St. Interior view. Both © Aidan Thomson.
St. Augustine†, Watling St., only the tower remains. © Aidan Thomson.

St. Bartholomew-the-Great, Smithfield (Priory Church). From an old postcard, Bulman Collection. A modern view. © Aidan Thomson. Link.
St. Bartholomew-the-Less, Smithfield. Interior view. Both © Aidan Thomson. Link.
St. Benet†, Paul's Wharf. Interior view. Both © Aidan Thomson. Link.
St. Botolph, Aldersgate. Interior view. Both © Aidan Thomson.
St. Botolph, Bishopsgate. © Aidan Thomson.

St. Catherine Cree (St. Katherine Cree in Betjeman). From an old postcard, Bulman Collection.
St. Clement†, Eastcheap. © Aidan Thomson.
St. Clement's Dane. An unusual night-time scene. Another view. Both from an old postcards, Bulman Collection.

St. Dunstan-in-the-East†. Of Wren, only the tower survives, the church having been bombed during WWII. TQ 332 807. © Andrew Ross.

St. Ethelburga, Bishopsgate. Interior view. Both © Aidan Thomson.
St. Etheldreda Ely (R.C.), Holborn. © Aidan Thomson.

St. Giles, Cripplegate. Interior view. Both © Aidan Thomson. Another view. © Murray Lynn.

St. Helen, Bishopsgate. Interior view. Both © Aidan Thomson. Link.

St. James†, at Garlickhythe. © Mark Summers. Link.
St. Joseph (R.C.). The church is in the basement. © Mark Summers. Link.

St. Lawrence Jewry†. © Tim Tomlinson. Another view. © David Gallimore. Link.

St. Magnus the Martyr† on Lower Thames St. © Mark Summers. Link.
St. Margaret Lothbury†. © Mark Summers. Link.
St. Margaret Pattens†. TQ 331 808. © Andrew Ross. Link.
St. Martin's within Ludgate†. © Bill Henderson. Another view. © Aidan Thomson.
St. Mary Abchurch†. Interior view. Both © Aidan Thomson. Link.
St. Mary Aldermary†. © Mark Summers. Link.
St. Mary Somerset, Upper Thames Street. © Mark Summers.
St. Mary-le-Bow, Cheapside. From an old postcard, Bulman Collection.
St. Mary-le-Strand. © Bill McKenzie. An old postcard view, Bulman Collection. The church in the background is probably St. Clement Dane. Link.
St. Mary's-at-Hill†. TQ 330 807. © Andrew Ross. Link.
St. Michael Cornhill† - in a very cramped location. By Wren (1672), tower by Hawksmoor (1722), restored by Gilbert (1860). © Mark Summers. Link.

The former St. Nicholas Cole Abbey†, now in use as a religious education centre. © Aidan Thomson. Two views (1, 2), both © David Gallimore. Link1. Link2.

St. Olave Jewry, in the City, is one of Wren's churches. It was demolished in 1888, leaving the tower only.  © Simon Kidner.
St. Olave, Hart Street, Aldgate. Samuel Pepys was a regular attendee here. The church was destroyed in the Blitz, but was later re-built. Thanks to Simon Kidner for clearing up my confusion regarding the two St. Olave's. From an old postcard, Bulman Collection. A modern view. © Mark Summers. Link1. Link2.

St. Paul's Cathedral†, from an old postcard, Bulman Collection. A distant high-level view, showing the cathedral as it's not possible to appreciate it from ground level. © Dave Westrap. Another view. © Aidan Thomson. Link.
St. Peter, Cornhill†. © Aidan Thomson. Link.

St. Sepulchre-without-Newgate†. Interior view. Both © Aidan Thomson. Link.
St. Stephen Walbrook†. TQ 326 809. © Andrew Ross. Link1. Link2.

St. Vedast-alias-Foster†, is near St. Paul's Cathedral. © Bill Henderson. Another view. © Aidan Thomson. Link.

Wesley's Chapel, City Road. © Tim Tomlinson. Link.

Balham
St. Mary and St. John the Divine, on Balham High Road. TQ 283 731. © Steve Bulman. Link.

Beckenham
St. Barnabas. Link is to a photo on the church website. 
St. George. 177 TQ 374 696. From an old postcard (franked 1905), Dave Westrap's Collection. Link1. Link2.
 

Beddington
St. Mary the Virgin. From an old postcard in Geoff Watt's Collection. Link.

Bermondsey
The Robert Browning Memorial Chapel, photographed in 1984. © Alan Taylor.

Bexley.

Bexleyheath
Bethany Hall on North Road. © Alan Taylor.

Bloomsbury.

Brentford
The former St. George, on Kew Bridge Road, which until recently housed a museum of musical instruments. © David Gallimore.

Brixton
St. Matthew. From an old postcard (franked 1919), Bulman Collection. A modern view, and another. Both © Tim Tomlinson.

Bromley
St. Peter and St. Paul. From an old postcard (franked 1909), Bulman Collection. Link.
Holmcroft Hall (photographed in 1984). © Alan Taylor.

Burnt Oak
St. Alphage. © Bill McKenzie.

Camden
Christ the King (Catholic Apostolic Church), Gordon Square. © Alan Taylor. Link.
St Pancras Church, Tavistock Place. © Bill McKenzie.
St Pancras Old Church, Pancras Road. © Bill McKenzie.

Chelsea

Chingford
St. Peter & St. Paul. From an old postcard, Bulman Collection.

Clapham & Clapham Common.

Clapton
Former Clapton Congress Hall (Salvation Army), From an old postcard, Rob Brettle's Collection.

Covent Garden
Corpus Christi (R.C.), Maiden Lane. © Bill Henderson. Link.
St. Paul. © Mark Summers. Link.

Crayford.

Denmark Hill
St. Matthew. From an old postcard, Bulman Collection.

Dulwich
Christ's Chapel, which serves Dulwich College. TQ 331 736. © Steve Bulman.

Ealing
St. Stephen. From an old postcard, Bulman Collection.

Erith
Cemetery Chapel, Erith Cemetery. 177 TQ 497 779. © Dave Westrap. Link.

Finchley

Finsbury Park
Pentecostal Holiness Church and Bible College. © Alan Taylor.

Friern Barnet

Fulham
Munster Park Wesleyan Church. From an old postcard in Reg Dosell's Collection.

Golders Green

Hampstead

Hampton Hill
St. James. The original postcard needed to be heavily processed to produce a still poor image, but it does show the impressive spire. The postcard dates from about 1905. © Jackie Blackman.

Hanworth
St. George. Link to external website.

Haringey
St. John the Baptist (Greek Orthodox). TQ 312 892. © Michael Bourne.

Harrow
All Saints (R.C.). TQ 183 888. © Michael Bourne. Link.
St. George at Headstone. Link to external website.

Hatch End.

Hendon.

Highgate.

Hillingdon
St. Margaret. From an old postcard, Bulman Collection.

Holborn
St. Alban the Martyr.

Hornsey

Islington.

Kentish Town
St. Silas the Martyr. © John Salmon.

Kensington.

Kenton
Methodist Church. TQ 173 887. © Michael Bourne.
St. Mary the Virgin. TQ 171 887. © Michael Bourne. Link.

Kew
St. Anne. From an old postcard (franked 1905), Bulman Collection. Link.

Kingsbury
Holy Innocents. TQ 208 885. © Michael Bourne.

King's Cross.

Lee
St. Margaret. From an old postcard, Bulman Collection. Link.

Little Stanmore
St. Lawrence Whitchurch. Previously in the "Unknown" section, and identified by Janet Gimber, the postcard (Bulman Collection) caption simply says "Whitchurch". Link1. Link2.

Marylebone.

Mayfair.

Mitcham
St. Peter & St. Paul. From an old postcard (franked 1905), Bulman Collection. Link.

Muswell Hill
U.R.C. TQ 283 896. © Michael Bourne.

New Cross
Hatcham Evangelical Church. © Alan Taylor.

North Finchley
St. Alban (R.C.). TQ 260 921. © Michael Bourne.

Northwood
Holy Trinity. From an old postcard (franked 1909), Bulman Collection.

Paddington.

Penge
Congregational Church. From an old postcard (franked 1932), Bulman Collection. Link.

Pentonville.

Pinner.

Plumstead
St. Margaret. One of London's lost churches, having been demolished in the 1960's. From an old postcard (franked 1907), Bulman Collection. The postcard only says "St. Margaret's - Plumstead", and since the card is franked "Woolwich", I'm making the assumption that this church is the Plumstead in London. If you think otherwise, please let me know.

Richmond
St. Mary Magdalene. From an old print, Shirley Beaumont's Collection. A modern view. © Shirley Beaumont. Link.

Romford.

St. Mary Cray
Temple Church. Dating from 1851, and replacing an earlier church, this church too was demolished (in 1954), following damage in WWII. Yet another church was built on the site (which today is U.R.C.). From an old postcard, Geoff Watt's Collection. Link.

St. Paul's Cray
St. Paulinus (redundant). From an old postcard, Bulman Collection.

Sanderstead
All Saints. From an old postcard, Geoff Watt's Collection.

Savoy
The Queen's Chapel of the Savoy. TQ 305 807. © Steve Bulman. Link.

Shepherd's Bush
St. Stephen. From an old postcard, Bulman Collection.

Shoreditch
The former St. Michael & All Angels, now used as a commercial building. © Mark Summers.

Sidcup.

Silvertown
St. Mark. © Ted Bagot (who, as a resident of New Zealand, is unquestionably the most distant contributor to this project).

Somers Town
St. Mary, built 1822-6, Eversholt St., NW1. St. Aloysius (R.C.), built 1966-8, corner of Eversholt St. and Phoenix Rd., NW1. Both © Peter Hobday.

Southwark.

Stoke Newington
Kingdom Hall of Jehovah's Witnesses. © George Weston.

Stratford
St. John. From an old postcard (franked 1916), Bulman Collection.

Streatham
Streatham Methodist Church. © Ray Harrington-Vail.

Streatham Hill
St. Margaret on Cricklade Avenue. © Tim Lomas. Link.
St. Simon and St. Jude (R.C.) on Hillside Road. © Tim Lomas. Link.

Surbiton
St. Mark. From an old postcard (franked 1908), Bulman Collection. Link.

Sutton
All Saints at Benhilton. From an old postcard (franked 1916), Bulman Collection. Link.

Totteridge
Union Church (U.R.C.). TQ 255 931. © Michael Bourne.

Twickenham
St. Mary. From an old engraving the © Colin Water's Collection. Link.

Upper Norwood
St. Aubyn (Congregational). From an old postcard (franked 1917), Bulman Collection.

Uxbridge
St. Andrew. From an old postcard, Bulman Collection.
St. Margaret. From an old postcard, Bulman Collection.

Walthamstow
St. Mary. From an old postcard, Bulman Collection.

Wanstead
Christ Church from an old postcard © Bulman Collection.
Wanstead Parish Church is not identified by name on this old postcard (Bulman Collection), but it is almost certainly of St. Mary, the description of which in Betjeman is very close to the picture. (Thanks to Graeme Exall for confirming that this is indeed St. Mary, and for this Link.)

Wembley.

Westminster.

Willesden
St. Mary. From an old postcard, Bulman Collection.

Woodside Park
St. Barnabas. TQ 256 924. © Michael Bourne.

Woolwich.