Use medium-size eggs to make these picnic and party favorites so they are small enough to serve as hors d'oeuvres.
Place eggs in a saucepan; cover with cold water. Bring to a boil; cook 1 minute. Remove from heat, and cover; let stand 13 minutes. Drain, and place in cold water until cool. Peel eggs, and slice in half lengthwise; separate the yolks from the whites. Trim curve off whites so they won't wobble. Set aside.
Place yolks in a sieve set over a medium bowl; press through with a spoon. Mix in mustard and mayonnaise; season with salt and pepper. Fill egg-white halves with yolk mixture. Cover with plastic wrap; refrigerate up to 4 hours. Before serving, garnish each with either parsley, paprika, or poppy seeds.