I make mine with mayo, brown mustard, mustard powder, onion powder, garlic powder, salt, and pepper and sprinkle with paprika. My mom leaves out the onion and garlic when she makes hers and about had a fit when she saw me doing it, but everybody likes them, so I leave it in!
Funny deviled egg story:
For the past couple years at family gatherings after the eggs have been served I've been seeing some eggs topped with an extra glob of filling and wondering where it was coming from. Turns out my little sister who always requests deviled eggs and claims to love them actually only likes the whites with the barest hint of filling, so she dumps out the middle on the next egg over so somebody else gets a double helping. Once I found that out, I asked why she didn't just request hard boiled eggs and save me the trouble, but she says they aren't party food like deviled eggs... It's a good thing I like eating them otherwise I'd stop making them at her request!