Norman Castles in Britain
Derek F. Renn
This is a standard text and actually quite readable. Has a very nice chapter on the building of Norman castles plus a good gazetteer of the Norman castles of Britain. It is now quite elderly and much has changed in castle studies since its publication but this remains useful, particularly for historical primary source references. The second edition has some addenda from the first making it the essential version.
547 sites in England.
155 sites in Wales.
3 sites in the Islands.
Published by John Baker/Humanities Press (1973 (second edition); London)
ISBN: 0 212 97002 X (UK) 0 391 00276 7 (USA)