When I was looking for old maps of the Isle of Man a couple of years ago, I came across a great source of old maps of towns across Britain and Ireland (as well as a couple of the Isle of Man and other places in Europe). I didn't mention them in the post (I perhaps hadn't found them at that point) but I've recently had a bit of an interest in the history of the area around where I'm living, so went back to this supplier to order some old maps of the Elephant and Castle area of London.
Alan Godfrey has been building up an impressive collection of reprints of old Ordnance Survey Maps from the late 19th Century and early 20th Century. The maps, collectively known as The Godfrey Edition, are reproductions of original maps, often scaled down slightly, but printed in extraordinary quality considering the age of the originals.
As described on their website:
Most of the maps are highly detailed, taken from the 1/2500 plans and reprinted at about 14 inches to the mile. They cover towns in great detail, showing individual houses, railway tracks, factories, churches, mills, canals, tramways and even minutiae such as dockside cranes, fountains, signal posts, pathways, sheds, wells, etc.. Each map includes historical notes on the area concerned. Many also include extracts from contemporary directories. The maps are neatly folded, often with an early photograph on the cover. The maps are ideal for local historians, transport historians, and family historians, or simply those with an interest in the town they live in or have visited. The maps are very good value and cost just £2.25 each.
Whenever I've bought maps from them (their whole catalog is online in their map shop) I've found them to be very responsive, with the maps often arriving the next day. Alan Godfrey was also open to the use of names from old maps for the OpenStreetMap project (where they were still relevant, as they often were in Peel in the Isle of Man, where much of the historical street layout still exists).
So, if you're interested in the history of the area around you, I highly recommend these maps as a great start to learning more about how things used to be.