Off the top of my head... an obscure one that I like would be "Jocasta" from the Avengers. She is an android built by Ultron (one of The Avengers' main villains) and infused with the personality of The Wasp (one of the main heroines). She starts out as evil but later turns good.
http://underworld.fortunecity.com/blood ... casta.html
I'll have to think of others. Wonder Woman is certainly a candidate, but one that's a little too obvious.
Great topic, Fin!