Great Britain's endgame study supremo is John Roycroft, founder of EG – an important magazine of the genre
Alexander Rueb Vereniging voor SchaakEindspelStudie – a Dutch association for endgame study enthusiasts – now with a newly-refurbished website by Peter Boll.
A website created by John and Sue Beasley. It includes a PDF archive of the full run of British Endgame Study News (BESN) (which ran from 1996 to 2010), a new presentation of Reti's endgame studies and much other chess composition content. Non-chess content includes music and a remarkable diary of Moravian village life.
A website by Brian Gosling that seeks to expound the endgame in chess. To help with this it quotes lots of endgame studies.
I am happy to add more links to the above list. Please just let me know about them.
Developed and maintained by Brian Stephenson.