8Martha Jones
Played by Freema Agyeman
Like Dodo in the classic series, Martha comes in for a lot of stick in the new series, most of which I think is unfair to both the character and the actress. While I would agree that she was sometimes written a bit poorly, I do think that the character really could have gone on to better things, had she been treated a bit better within the show.
After the departure of Rose, the Doctor decided to mope. And mope and mope and mope. His moping meant that Martha really never stood a chance. Episode after episode he kept reminding her, and also the audience, that she wasn't Rose and that he didn't want her around. It took almost half the season before he finally accepted her as his companion and by that time the damage was done and the audience just didn't take to her. I think if the Doctor had been more accepting of her then so would the viewing public.
What people seem to forget though, is that Martha was strong and mature and independent and I think personally, far superior to Rose who came before her. She didn't have a long run in the show and she didn't manage to win over the public, but I think had she had more time to develop and better treatment from the writers then she could have been amazing.