The Inventories of the Royal Commission of the Ancient and Historic Monuments in Wales and Monmouthshire and of the Royal Commission of Historic Monuments of England. These inventories of monuments have been published on a county bases since the early 20th century. David Cathcart King was pretty damning about the quality of the early inventories, particularly those of Wales, but the later inventories are an invaluable resource; in particular the two Inventories of Castles in Glamorgan, mainly the work of Jack Spurgeon, are excellent.
Published volumes are
WALES;
RCAHMW, 1911, An inventory of the Ancient Monuments of Montgomery
RCAHMW, 1912, An inventory of the Ancient Monuments of Flintshire
RCAHMW, 1913, An inventory of the Ancient Monuments of Radnorshire
RCAHMW, 1914, An inventory of the Ancient Monuments of Denbighshire
RCAHMW, 1917, An inventory of the Ancient Monuments of Carmarthenshire
RCAHMW, 1921, An inventory of the Ancient Monuments of Merionethshire
RCAHMW, 1925, An inventory of the Ancient Monuments of Pembrokeshire
RCAHMW, 1937, An inventory of the Ancient Monuments of Anglesey
RCAHMW, 1956, A survey and inventory of the Ancient Monuments of Caernarvonshire Vol. 1: east
RCAHMW, 1960, A survey and inventory of the Ancient Monuments of Caernarvonshire Vol. 2: central
RCAHMW, 1964, A survey and inventory of the Ancient Monuments of Caernarvonshire Vol. 3: west
RCAHMW, 1976, An Inventory of the Ancient Monuments in Glamorgan Vol. 1 pt. 2
RCAHMW, 1981, An Inventory of the Ancient Monuments in Glamorgan Vol. 4 pt. 1: The Greater Houses
RCAHMW, 1982, An Inventory of the Ancient Monuments in Glamorgan Vol. 3 pt. 2: Secular Non-defensive Monuments
RCAHMW, 1991, An Inventory of the Ancient Monuments in Glamorgan Vol. 3 pt. 1a: The Early Castles
RCAHMW, 2000, An Inventory of the Ancient Monuments in Glamorgan Vol. 3 pt. 1b: The Later Castles

ENGLAND
RCHME, 1912, An inventory of the historical monuments in Buckinghamshire Vol. 1: south
RCHME, 1913, An inventory of the historical monuments in Buckinghamshire Vol. 2: north
RCHME, 1959, An inventory of historical monuments in the City of Cambridge
RCHME, 1968, An inventory of historical monuments in the County of Cambridgeshire Vol. 1: west Cambridgeshire
RCHME, 1972, An inventory of historical monuments in the County of Cambridgeshire Vol. 2: north-east Cambridgeshire
RCHME, 1952, An inventory of historical monuments in the County of Dorset Vol. 1: west
RCHME, 1970, An inventory of historical monuments in the County of Dorset Vol. 2: south-east
RCHME, 1970, An inventory of historical monuments in the County of Dorset Vol. 3: central
RCHME, 1972, An inventory of historical monuments in the County of Dorset Vol. 4: north
RCHME, 1975, An inventory of historical monuments in the County of Dorset Vol. 5: east
RCHME, 1916, An inventory of the historical monuments in Essex Vol. 1: north-west
RCHME, 1921, An inventory of the historical monuments in Essex Vol. 2: central and south-west
RCHME, 1922, An inventory of the historical monuments in Essex Vol. 3: north-east
RCHME, 1923, An inventory of the historical monuments in Essex Vol. 4: south-east
RCHME, 1931, An inventory of the historical monuments in Herefordshire Vol. 1: south-west
RCHME, 1932, An inventory of the historical monuments in Herefordshire Vol. 2: east
RCHME, 1934, An inventory of the historical monuments in Herefordshire Vol. 3: north-west
RCHME, 1910, An inventory of the historical monuments in Hertfordshire
RCHME, 1926, An inventory of the historical monuments in Huntingdonshire
RCHME, 1925, Inventory of Historic Monuments in London Vol. 2: West London
RCHME, 1930, Inventory of Historic Monuments in London Vol. 5: East London
RCHME, 1937, An inventory of the historical monuments in Middlesex
RCHME, 1975, An inventory of the historical monuments in the County of Northampton Vol. 1: north-east
RCHME, 1979, An inventory of the historical monuments in the County of Northampton Vol. 2: central
RCHME, 1981, An inventory of the historical monuments in the County of Northampton Vol. 3: north-west
RCHME, 1982, An inventory of the historical monuments in the County of Northampton Vol. 4: south-west
RCHME, 1985, An inventory of the historical monuments in the County of Northampton Vol. 5: Northampton
RCHME, 1977, ‘Castle’ and ‘Town walls' in An Inventory of Historical Monuments: the Town of Stamford
RCHME, 1939, Inventory-City of Oxford
RCHME, 1980, ‘Old Sarum’, in Ancient and Historical Monuments in the City of Salisbury Vol. 1
RCHME, 1936, An inventory of the historical monuments in Westmorland
RCHME, 1972, An Inventory of the Historical Monuments in the City of York Vol. 2: The Defences_
RCHME, 1975, An Inventory of the Historical Monuments in the City of York Vol. 4: the North-east_