As far as names go, they don't get much bigger than Steven Jackson. As far as positions go, they don't have a shorter shelf life than running back.
Jackson has been one of the best running backs in the game for the past nine years. He is coming up on that dreaded 30 year threshold when backs begin to wear down. Not the best time for him to have to head into free agency.
In Oakland, they could use a big, bruising back like Jackson. He would share duties with Darren McFadden which could prolong his effectiveness. He is also still a 1000 yard rusher who averages over four yards per carry so if/when McFadden gets injured, he could easily carry the load just as he has done his entire career. A career in which he has had over 1000 yards every season but his rookie season.
Jackson also could have serious interest in coming to Oakland. His best season was in 2006 when he ran for 1528 yards under the guidance of offensive coordinator, Greg Olson who is now the offensive coordinator in Oakland. The two know each others' strengths and both could prolong each others' careers should they get back together.
Here is what Tevin Broner of Rams blog, Turf Show Times had to say:
Stephen Jackson is everything you're thinking; big, strong, physical, not fast or elusive, but he's getting up there in years. He doesn't get many touchdowns, but he's a 1,000 yard rusher for the next two years, or close to it. Also good at picking up the blitz. The Rams met with Jackson at the combine and in my opinion there's a 60/40 chance he will return.