The obvious answer is James Cook. He's going to finish as atop 10 back this year if he stays healthy.
For a less than obvious answer: If Dorian Williams finds snaps he is going to flash big time this year. The hype about his instincts....isn't hype.
Another less obvious answer: Damar. While some pundits ponder what happens if we release him...guy had 88 tackles and 1.5 sacks last year while still being very inexperienced. The was he played today: fast and without hesitation. Another guy that if pressed into snaps is going to continue to get better. Really wouldn't surprise me much if he's a starting S on this team beginning next year.