There are a handful of costumes I see at every convention I attend. Harley Quinn is currently at the top of that list, but Sailor Scouts from Sailor Moon are popular too. Sailor Moon is the one I spot most frequently, but I see several others and sometimes entire group cosplays. Tsuri, a.k.a. JS Cosplay, makes a terrific Super sailor Mars. She used a pattern from Maia/NyuNyu Cosplay and sewed the entire costume by hand:
Body suit made from 4 way stretch milliskin matte spandex, red is a cotton sateen, arm bands made with piping cord filler. Interface used for the bow.
Her wig is from Epic Cosplay, and for the sake of time, she purchased Sailor Mars accessories from Unique Cosplay Props.