Project European Royalty

Belgium
Complete, see Monarchs of Belgium

Denmark
Complete from Christian I of Denmark (1426-1481) onwards

England and the United Kingdom
Complete from William the Conqueror onwards, erratic before that

France
Complete, see Monarchs of France

Germany
Complete, see Monarchs of Germany -- note that the kings of Hanover, Saxony etc are not yet there

The Netherlands
Complete, see Monarchs of the Netherlands

Scotland
Completed from David I onwards, erratic before that