I am partial to a horseradish sauce my grandmother (Czech) made:

Grated Horseradish
Make apple sauce by grating apples
mix together with a touch of salt and some sugar to sweeten
a little bit of vinegar

Great on ham and also cold calves tongue (that is great cooked with a brown sauce - the horseradish/apple sauce is with the left overs.

Of course, you can simplify and use pre-made apple sauce (and horseradish for that matter) but I prefer freshly grated apples.