The list has no particular order but my favorites for you to cosplay would be the two first ones but all the other ones are also amazing!
CatwomanDC COMICS
So she's one of my favorites too. I mean just look at her, she's probably one of the sexiest villainess (i love the mask and all).
It's not an easy costume but i can ask my mum, she'll probably be able to do something.
And the good thing is that, with Poison Ivy and my Harley she's a member of the Sirens of Gotham, so Catwoman and Harley are canon.
Poison Ivy[/b]DC COMICS
God, I really love her too but she has different versions of her costume and i don't like them all. But something like that is sooooo gorgeous:
and can be very easy to make, you'll need a ginger wig or to dye your hair but she can be very very very cool to cosplay.
And her with Harley is even more canon, a lot of people ship them together and she has been a very important friend and help to Harley :
Lady BlackhawkDC COMICS
Really badass, like any girl from Birds of Prey. The costume might be too difficult to sew but i think we should be able to find it by piece, like buying the skirt and the jacket separately.
Black CanaryDC COMICS
Just like Lady Blackhawk because she's a Bird of Prey, costume should be easy to make (but maybe a little less-sexy one ahaha)
Black WidowMARVEL
Well she's your wife so you know her. The costume is almost the same as catwoman so if we can do catwoman's we can do natasha's
Emma FrostMARVEL
You know her from First Class. There are so many version of her costume that it should be easy to get or make one.
She-HulkMARVEL
Aha yes, female version of Hulk but hey, she's soooooo badass, i really love her. The costume is very very easy but you'd have to paint your body in green.
HarlequinDC COMICS
So to be honest i don't really know her but it could be fun to cosplay her when i'm Harley Quinn, as they're kind of similar.
Also (but maybe more difficult to cosplay) : Zatanna, Wonder Woman, Rogue, Ms Marvel, Huntress...