Julia's butter, of course, and mayo, Dijon mustard, S&P, chopped pickle or relish, minced onion,
and after stuffing, a generous sprinkle of paprika.
Regardless of the recipe, I think the most important factor is to not overcook the eggs in the first place. Tender whites stuffed with creamy, soft yolks (no gray discoloring) are irresistable.
I'm ALWAYS in the mood for them, and in my experience a platter or them, no matter how large, never lasts more than a few minutes.