Brandon Jacobs.
You'll be able to get him cheaply, and he's backing up Tiki, who is now 32 yrs old, is small by NFL RB standards (5'-10", 200 lbs dripping wet), and gets tons of work. I used to say the same thing about Jordan when he was with the Jets behind the aging CuMar and that didn't work out, I know, but Barber is playing against the odds.
Jacobs is huge, has very good speed, scores TDs even when Barber is healthy, and catches well out of the backfield. If Barber does get hurt or slow down - and with his age, size, and workload going against him in combination it is more probable than other featured RBs - Jacobs could be a very nice late pickup.
I'd keep a close eye on Orlovsky late in drafts, too. Mad Mikey is in charge of the DET O, which has some decent weapons. If Harington falters at all or gets whacked, Orlovsky may spring out of nowhere & put up some very good numbers.