Fate/stay night, Saber gets extra points for not only having a fancy dress, particularly the gold trimming, but one that's further pimped out with plate mail. It's to be expected, though: most of the examples here are merely princesses, while Saber is a king. King Arthur, to be precise.
In Fate/Nuovo Guerra, Lempicialynn wears a red dress trimmed with black frills, and Lumivellamo wears a blue dress with white trimming and frills.
Another is a purple dress with ruffled trimming, darker purple underskirt, puff sleeves, white Opera Gloves, and a lace-trimmed choker.
The witches of Umineko no Naku Koro ni all seem to get this, as well as one or two members of the Ushiromiya family.
Beatrice's dress is one of the most elaborate◊. It's a dark brown dress with large orange symbols and trimming, a dark red ruched petticoat, puff sleeves, a small pink bow, and white flounces. As a child◊, she wore a dark red dress with puff sleeves and two large white sashes that tied at the back and fell down like a cape.
Bernkastel wears a blue and white dress◊ with ruffles, flared sleeves, a large blue bow at the neck, and a double tiered underskirt.
Lambdadelta wears a pink dress◊ with pink ruffles, red bows, black opera gloves, puff sleeves, and a pumpkin decoration on the waist.
Virgilia wears a black dress◊ with white ruffles, a white ruffled petticoat, and a nice hat with red flowers and white ruffles under the brim.
Eva-Beatrice wears a purple and black dress◊ with ruffles, underskirt, opera gloves, a large red bow on the waist, and a ruffled hat with a red rose on the side.
Featherine wears two◊. One is a pink kimono with a bell skirt, opera gloves, and a green sash with medals decorating it. The other is a brown dress with lots of white frill trimming, and a gold sash with a green jewel clasping it together.
Shannon◊ has one skirt on top of a miniskirt, a corset, and several buckles. And she's just a servant.
Natsuhi wears a dress with at least three layers in the skirt, each cut to show the other layers. In the manga, she wears an even more frilly dress.