Notes and papers on orthodox chess (John)
British Endgame Study News (ISSN 1393-0318, 1996-2010)
Depth and Beauty (the endgame studies of Artur Mandler)
The chess endgame studies of Richard Réti
PGN file containing all reciprocal zugzwangs with not more than six men
51 Flights of Chess Fancy (chapters 1-3/5 refer)
Reminiscences of a puzzle enthusiast (pages 1-5/12 refer)
The ARVES site www.arves.org and Brian Gosling's site www.chessending.com provide a great deal of further material on chess endgame studies, and Brian Stephenson's site www.bstephen.me.uk is an excellent lead-in to chess composition in general.