A few years ago the Account Book of the Paymaster General of the army of William III for the year 1690 was discovered in the Belfast City Hall. See for example
This Account Book by Paymaster General Thomas Coningsby lists the payments made to the regiments in William III's army, and those made to hospitals, intelligence, etc.
It is a bit unfortunate and strange that this document is kept by the Grand Orange Lodge of Ireland in Belfast, and not by an institution like the Public Records Office of Northern Ireland.
Nevertheless, this Orange Lodge made a rather nice workbook based on this Account Book. Though aimed at children, it will be nice for adults too: paymaster-general-workbook.pdf. Unfortunately there is no further information regarding accessibility of this Account Book for researchers. I truly hope this document is not abused for pursuing a political agenda.
Contrary to rumours and gossip, this Account Book does not contain the names of all men in William III's army. It does, however, contain the names of about 400 officers. With about 40 officers in a regiment of foot, this means that this Account Book does neither contain all officers in William III's.
But anyway, let's hope that the information in this document will become available soon!