Often times I just use a random "extra" type costume (random dark fairy, random gypsy, random ninja), since I find costumes difficult to do sometimes due to my figure, long hair, and tan skin. I make it work as much as I can.
More specifically, I've also dressed up as Hinata from Naruto, Sailor Pluto for Sailor Moon (and I also technically did sailor moon, but that was mostly for the hair tutorial I was doing). Costumes not based on anime or manga include Jasmine from Aladdin, Sif from Thor (Marvel movie 'verse), Cimorene from Dealing with Dragons, both Parvati and Padma Patil from Harry Potter (I switched ties and badges every half hour and introduced myself differently, to the confusion of everyone at that party), and right now I'm working on a fem!Castiel from SPN, fem!Sherlock (BBC), and a fem!Tony Stark (though I'm having a heard time with it and will probably just go with an armourless, suited version instead of trying to make armor that will fit me). less