Regular reader of this blogs will be aware i'm interested in old chuches. If you are a regular reader and hadn't noticed I dispair.
Anyway I've come across two pocket sized guides to the City of London churches. When we refere to the city of London we are referring to the historic core off London. It was originally defined by the old Roman Walls but has grown slightly over the years.
Today the city is synonomous with the financial core which is often referred to as the square mile.
The two guides are The Visitor's Guide to the City of London Churches by Tony Tucker published by the friends of the city churches. It covers 47 churches, 2 ruins and 8 towers it has a map some photos and is generally pretty good. London's City Churches by Stephen Millar also features 47 towers and 8 towers. The 47 exclude at least one church in the Tucker but includes St pauls cathedral. it two has maps but features a couple of walks and opening times (Monday-Friday they are seldom open saturday and sunday). The city churches no longer have parishes but get used for workers in the city.
If pushed to use one i'd take Millar but urge you to check out the one it misses (st Ethelreda Holborn - not technically in the city). Because of the Great Fire of 1666 many medieval churces were destroyed but here is a very fine collection of churches by Wren (and some Cathedral he worked on ;) ).
If you are in the area you can have a fascinating day checking out the churches here and there is some fabulous architecture in the area. I have to be in the city early December so my little compact will give you a tour of one or two.