This isn't my list, but over on Rivals, a well regarded poster named Jim_S put up his list of the best running backs at Michigan since 1969. I'm not old enough to remember a bunch of these guys, so I can't really say whether he's right or wrong with a lot of them. But I think it's an interesting list nonetheless. Take a look and see what you think.
BTW, he said this is not "who had the best career at Michigan" or "who had the best NFL career." He seems to basically be talking about the most talented running backs if you were trying to build a team.