I am an OS map addict - I scour charity shops and junk shops for secondhand copies.
Coincidentally, I just posted a few notes on maps in another thread. I pointed out that when out walking the OS 1:25000 scale 'Explorer' series is more useful than the 1:50000 'Landranger' series (the 1:25K maps have field boundaries marked so you can use them to navigate and see which side of them you should be on).
I also recommend the Ordnance Survey's Get A Map service.
I bought a second hand copy of an O/S special map on the Hadrian's Wall in one of our local shops. It seemed to be about 20 years old but it overlaid a map of the wall's route, along with interesting Roman sites over a modern map of the area. It was quite interesting as relatively little of the wall remains now so its often hard to imagine its precise route, especially in places like Newcastle.
Hi, if you like maps you may be interested in this site, if you zoom in on the map you end up with an ordanance survey map of the whole of Great Britain, and its printable. Much better than the 'Get a map' service offered by OS map site.