Modern OS maps
Modern OS Landranger and Street mapping on CCS website
Landranger and aerial views on Where's the Path
Irish On-line Mapping and Aerial Photography
Historic OS maps
One-inch New Popular Edition of England and Wales at CCS Sheetfinder
One-inch 1st, 2nd and 3rd edition Scotland and Scottish Popular at CCS Sheetfinder
One-inch Seventh Series of UK at CCS Sheetfinder
1:25,000 Provisional edition of UK at CCS Sheetfinder
Scotland - all series and scales at National Library of Scotland
New Popular Edition of England and Wales and Scottish Popular at NPE site
1:25,000 of Great Britain 1937-1961 (NLS)
Ten-mile to inch Planning maps of Britain 1944-1960 (NLS)
Seventh Series One-inch maps of Britain 1952-1961 (NLS)
Other maps - British Isles
Old Series one inch geological solid and drift maps for England and Wales (BGS)
Open Street Map - Open source map of UK
People's Map - Open source map of UK
SABRE - includes historic OS and Bartholomew maps
TfL London bus, tube, rail and river maps
Traveline Public transport maps of all UK and NI
Streetmap.co.uk - includes OS Explorer 1:25,000 mapping
MAGIC map – Multi Agency Geographic Information for the Countryside
Vision of Britain - maps, statistical trends and historical descriptions