Captain Marvel:
Carol Danvers, subjected to large amounts of lethal radiation, which transformed her into a warrior. She donned the mantle of Captain Marvel and is now the member of the Avengers. She is another strong contender who might get a standalone movie.
Scarlett Witch:
She is one of the most devastating mutants who possess supernatural powers to manipulate reality, she is a sister of Quicksilver, daughter of Magneto and mother to Wiccan and speed. She had a sizeable role in Avengers: Age of Ultron and will be next seen in Captain America: Civil War. She is unlikely to get a solo movie anytime soon.