I'll tell you who actually intrigues me, even though it would make people around here groan: Toby Gerhart.
I think the comparison to Peterson has made him look worse than he actually is, because this is a guy who's averaged 4.7 yards per carry for his career (compared to 5.0 for Peterson), including 7.9 ypc last year. He had a huge workload in college but in the pros he's never had more than 109 attempts in a season (average 4.9 ypc that year), which means he should have a ton of tread left on the tires (he'll be 27 in March).
I think this is my new favorite FA running back. He'd complement well with Miller and probably relish the chance to get more work than he's had in Minnesota. Plus you wouldn't think he'd cost very much.