Steven Jackson is going to miss 2 to 3 games with a partially torn groin, so the top 4 backs are a mess, but LJ had the exact same situation last year, and he still had 1750 yds and 18 TDs. Edwards is not going to change his philosophy of running LJ into the ground with another 400 plus carries. At the current rate that backs are dropping and the way some coaches are relying on the 2 back system, LJ is still a better bet than most, as he is going to be getting most of his team's carries.
There really is no one out there to get decent value for him, especially right now, where everyone thinks he is going to get nothing. Really, the most valuable back out there right now is Brian Westbrook, with the most reliable (read consistent) being Peterson, Addai, Barber III, and Lamont Jordan. With a lot of offenses inexplicably not running the ball (I was appalled to see how few carries most backs got last week), it makes the RB position very volatile right now. But, as a caveat, Johnson has proven himself and been very consistent for the past 3 seasons, while Westbrook has always carried injury issues (but been fairly consistent), Peterson could hit the rookie wall, Addai is a 2nd year guy carrying a full load as a feature for the first time, Barber III shares carries with Julius Jones (although he is definitely a better back), and Lamont Jordan has been wildly inconsistent since joining the league.
It's really a tough choice, as well as a personal preference, but LJ has proven himself time and again, even with a poor offense.
In any case, good luck.